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mmu.c
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mmu.c
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// SPDX-License-Identifier: GPL-2.0-only
/*
* Kernel-based Virtual Machine driver for Linux
*
* This module enables machines with Intel VT-x extensions to run virtual
* machines without emulation or binary translation.
*
* MMU support
*
* Copyright (C) 2006 Qumranet, Inc.
* Copyright 2010 Red Hat, Inc. and/or its affiliates.
*
* Authors:
* Yaniv Kamay <yaniv@qumranet.com>
* Avi Kivity <avi@qumranet.com>
*/
#include "irq.h"
#include "mmu.h"
#include "x86.h"
#include "kvm_cache_regs.h"
#include "kvm_emulate.h"
#include "cpuid.h"
#include <linux/kvm_host.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/highmem.h>
#include <linux/moduleparam.h>
#include <linux/export.h>
#include <linux/swap.h>
#include <linux/hugetlb.h>
#include <linux/compiler.h>
#include <linux/srcu.h>
#include <linux/slab.h>
#include <linux/sched/signal.h>
#include <linux/uaccess.h>
#include <linux/hash.h>
#include <linux/kern_levels.h>
#include <linux/kthread.h>
#include <asm/page.h>
#include <asm/memtype.h>
#include <asm/cmpxchg.h>
#include <asm/e820/api.h>
#include <asm/io.h>
#include <asm/vmx.h>
#include <asm/kvm_page_track.h>
#include "trace.h"
extern bool itlb_multihit_kvm_mitigation;
static int __read_mostly nx_huge_pages = -1;
#ifdef CONFIG_PREEMPT_RT
/* Recovery can cause latency spikes, disable it for PREEMPT_RT. */
static uint __read_mostly nx_huge_pages_recovery_ratio = 0;
#else
static uint __read_mostly nx_huge_pages_recovery_ratio = 60;
#endif
static int set_nx_huge_pages(const char *val, const struct kernel_param *kp);
static int set_nx_huge_pages_recovery_ratio(const char *val, const struct kernel_param *kp);
static struct kernel_param_ops nx_huge_pages_ops = {
.set = set_nx_huge_pages,
.get = param_get_bool,
};
static struct kernel_param_ops nx_huge_pages_recovery_ratio_ops = {
.set = set_nx_huge_pages_recovery_ratio,
.get = param_get_uint,
};
module_param_cb(nx_huge_pages, &nx_huge_pages_ops, &nx_huge_pages, 0644);
__MODULE_PARM_TYPE(nx_huge_pages, "bool");
module_param_cb(nx_huge_pages_recovery_ratio, &nx_huge_pages_recovery_ratio_ops,
&nx_huge_pages_recovery_ratio, 0644);
__MODULE_PARM_TYPE(nx_huge_pages_recovery_ratio, "uint");
/*
* When setting this variable to true it enables Two-Dimensional-Paging
* where the hardware walks 2 page tables:
* 1. the guest-virtual to guest-physical
* 2. while doing 1. it walks guest-physical to host-physical
* If the hardware supports that we don't need to do shadow paging.
*/
bool tdp_enabled = false;
static int max_page_level __read_mostly;
enum {
AUDIT_PRE_PAGE_FAULT,
AUDIT_POST_PAGE_FAULT,
AUDIT_PRE_PTE_WRITE,
AUDIT_POST_PTE_WRITE,
AUDIT_PRE_SYNC,
AUDIT_POST_SYNC
};
#undef MMU_DEBUG
#ifdef MMU_DEBUG
static bool dbg = 0;
module_param(dbg, bool, 0644);
#define pgprintk(x...) do { if (dbg) printk(x); } while (0)
#define rmap_printk(x...) do { if (dbg) printk(x); } while (0)
#define MMU_WARN_ON(x) WARN_ON(x)
#else
#define pgprintk(x...) do { } while (0)
#define rmap_printk(x...) do { } while (0)
#define MMU_WARN_ON(x) do { } while (0)
#endif
#define PTE_PREFETCH_NUM 8
#define PT_FIRST_AVAIL_BITS_SHIFT 10
#define PT64_SECOND_AVAIL_BITS_SHIFT 54
/*
* The mask used to denote special SPTEs, which can be either MMIO SPTEs or
* Access Tracking SPTEs.
*/
#define SPTE_SPECIAL_MASK (3ULL << 52)
#define SPTE_AD_ENABLED_MASK (0ULL << 52)
#define SPTE_AD_DISABLED_MASK (1ULL << 52)
#define SPTE_AD_WRPROT_ONLY_MASK (2ULL << 52)
#define SPTE_MMIO_MASK (3ULL << 52)
#define PT64_LEVEL_BITS 9
#define PT64_LEVEL_SHIFT(level) \
(PAGE_SHIFT + (level - 1) * PT64_LEVEL_BITS)
#define PT64_INDEX(address, level)\
(((address) >> PT64_LEVEL_SHIFT(level)) & ((1 << PT64_LEVEL_BITS) - 1))
#define PT32_LEVEL_BITS 10
#define PT32_LEVEL_SHIFT(level) \
(PAGE_SHIFT + (level - 1) * PT32_LEVEL_BITS)
#define PT32_LVL_OFFSET_MASK(level) \
(PT32_BASE_ADDR_MASK & ((1ULL << (PAGE_SHIFT + (((level) - 1) \
* PT32_LEVEL_BITS))) - 1))
#define PT32_INDEX(address, level)\
(((address) >> PT32_LEVEL_SHIFT(level)) & ((1 << PT32_LEVEL_BITS) - 1))
#ifdef CONFIG_DYNAMIC_PHYSICAL_MASK
#define PT64_BASE_ADDR_MASK (physical_mask & ~(u64)(PAGE_SIZE-1))
#else
#define PT64_BASE_ADDR_MASK (((1ULL << 52) - 1) & ~(u64)(PAGE_SIZE-1))
#endif
#define PT64_LVL_ADDR_MASK(level) \
(PT64_BASE_ADDR_MASK & ~((1ULL << (PAGE_SHIFT + (((level) - 1) \
* PT64_LEVEL_BITS))) - 1))
#define PT64_LVL_OFFSET_MASK(level) \
(PT64_BASE_ADDR_MASK & ((1ULL << (PAGE_SHIFT + (((level) - 1) \
* PT64_LEVEL_BITS))) - 1))
#define PT32_BASE_ADDR_MASK PAGE_MASK
#define PT32_DIR_BASE_ADDR_MASK \
(PAGE_MASK & ~((1ULL << (PAGE_SHIFT + PT32_LEVEL_BITS)) - 1))
#define PT32_LVL_ADDR_MASK(level) \
(PAGE_MASK & ~((1ULL << (PAGE_SHIFT + (((level) - 1) \
* PT32_LEVEL_BITS))) - 1))
#define PT64_PERM_MASK (PT_PRESENT_MASK | PT_WRITABLE_MASK | shadow_user_mask \
| shadow_x_mask | shadow_nx_mask | shadow_me_mask)
#define ACC_EXEC_MASK 1
#define ACC_WRITE_MASK PT_WRITABLE_MASK
#define ACC_USER_MASK PT_USER_MASK
#define ACC_ALL (ACC_EXEC_MASK | ACC_WRITE_MASK | ACC_USER_MASK)
/* The mask for the R/X bits in EPT PTEs */
#define PT64_EPT_READABLE_MASK 0x1ull
#define PT64_EPT_EXECUTABLE_MASK 0x4ull
#include <trace/events/kvm.h>
#define SPTE_HOST_WRITEABLE (1ULL << PT_FIRST_AVAIL_BITS_SHIFT)
#define SPTE_MMU_WRITEABLE (1ULL << (PT_FIRST_AVAIL_BITS_SHIFT + 1))
#define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level)
/* make pte_list_desc fit well in cache line */
#define PTE_LIST_EXT 3
/*
* Return values of handle_mmio_page_fault and mmu.page_fault:
* RET_PF_RETRY: let CPU fault again on the address.
* RET_PF_EMULATE: mmio page fault, emulate the instruction directly.
*
* For handle_mmio_page_fault only:
* RET_PF_INVALID: the spte is invalid, let the real page fault path update it.
*/
enum {
RET_PF_RETRY = 0,
RET_PF_EMULATE = 1,
RET_PF_INVALID = 2,
};
struct pte_list_desc {
u64 *sptes[PTE_LIST_EXT];
struct pte_list_desc *more;
};
struct kvm_shadow_walk_iterator {
u64 addr;
hpa_t shadow_addr;
u64 *sptep;
int level;
unsigned index;
};
#define for_each_shadow_entry_using_root(_vcpu, _root, _addr, _walker) \
for (shadow_walk_init_using_root(&(_walker), (_vcpu), \
(_root), (_addr)); \
shadow_walk_okay(&(_walker)); \
shadow_walk_next(&(_walker)))
#define for_each_shadow_entry(_vcpu, _addr, _walker) \
for (shadow_walk_init(&(_walker), _vcpu, _addr); \
shadow_walk_okay(&(_walker)); \
shadow_walk_next(&(_walker)))
#define for_each_shadow_entry_lockless(_vcpu, _addr, _walker, spte) \
for (shadow_walk_init(&(_walker), _vcpu, _addr); \
shadow_walk_okay(&(_walker)) && \
({ spte = mmu_spte_get_lockless(_walker.sptep); 1; }); \
__shadow_walk_next(&(_walker), spte))
static struct kmem_cache *pte_list_desc_cache;
static struct kmem_cache *mmu_page_header_cache;
static struct percpu_counter kvm_total_used_mmu_pages;
static u64 __read_mostly shadow_nx_mask;
static u64 __read_mostly shadow_x_mask; /* mutual exclusive with nx_mask */
static u64 __read_mostly shadow_user_mask;
static u64 __read_mostly shadow_accessed_mask;
static u64 __read_mostly shadow_dirty_mask;
static u64 __read_mostly shadow_mmio_mask;
static u64 __read_mostly shadow_mmio_value;
static u64 __read_mostly shadow_mmio_access_mask;
static u64 __read_mostly shadow_present_mask;
static u64 __read_mostly shadow_me_mask;
/*
* SPTEs used by MMUs without A/D bits are marked with SPTE_AD_DISABLED_MASK;
* shadow_acc_track_mask is the set of bits to be cleared in non-accessed
* pages.
*/
static u64 __read_mostly shadow_acc_track_mask;
/*
* The mask/shift to use for saving the original R/X bits when marking the PTE
* as not-present for access tracking purposes. We do not save the W bit as the
* PTEs being access tracked also need to be dirty tracked, so the W bit will be
* restored only when a write is attempted to the page.
*/
static const u64 shadow_acc_track_saved_bits_mask = PT64_EPT_READABLE_MASK |
PT64_EPT_EXECUTABLE_MASK;
static const u64 shadow_acc_track_saved_bits_shift = PT64_SECOND_AVAIL_BITS_SHIFT;
/*
* This mask must be set on all non-zero Non-Present or Reserved SPTEs in order
* to guard against L1TF attacks.
*/
static u64 __read_mostly shadow_nonpresent_or_rsvd_mask;
/*
* The number of high-order 1 bits to use in the mask above.
*/
static const u64 shadow_nonpresent_or_rsvd_mask_len = 5;
/*
* In some cases, we need to preserve the GFN of a non-present or reserved
* SPTE when we usurp the upper five bits of the physical address space to
* defend against L1TF, e.g. for MMIO SPTEs. To preserve the GFN, we'll
* shift bits of the GFN that overlap with shadow_nonpresent_or_rsvd_mask
* left into the reserved bits, i.e. the GFN in the SPTE will be split into
* high and low parts. This mask covers the lower bits of the GFN.
*/
static u64 __read_mostly shadow_nonpresent_or_rsvd_lower_gfn_mask;
/*
* The number of non-reserved physical address bits irrespective of features
* that repurpose legal bits, e.g. MKTME.
*/
static u8 __read_mostly shadow_phys_bits;
static void mmu_spte_set(u64 *sptep, u64 spte);
static bool is_executable_pte(u64 spte);
static union kvm_mmu_page_role
kvm_mmu_calc_root_page_role(struct kvm_vcpu *vcpu);
#define CREATE_TRACE_POINTS
#include "mmutrace.h"
static inline bool kvm_available_flush_tlb_with_range(void)
{
return kvm_x86_ops.tlb_remote_flush_with_range;
}
static void kvm_flush_remote_tlbs_with_range(struct kvm *kvm,
struct kvm_tlb_range *range)
{
int ret = -ENOTSUPP;
if (range && kvm_x86_ops.tlb_remote_flush_with_range)
ret = kvm_x86_ops.tlb_remote_flush_with_range(kvm, range);
if (ret)
kvm_flush_remote_tlbs(kvm);
}
static void kvm_flush_remote_tlbs_with_address(struct kvm *kvm,
u64 start_gfn, u64 pages)
{
struct kvm_tlb_range range;
range.start_gfn = start_gfn;
range.pages = pages;
kvm_flush_remote_tlbs_with_range(kvm, &range);
}
void kvm_mmu_set_mmio_spte_mask(u64 mmio_mask, u64 mmio_value, u64 access_mask)
{
BUG_ON((u64)(unsigned)access_mask != access_mask);
BUG_ON((mmio_mask & mmio_value) != mmio_value);
shadow_mmio_value = mmio_value | SPTE_MMIO_MASK;
shadow_mmio_mask = mmio_mask | SPTE_SPECIAL_MASK;
shadow_mmio_access_mask = access_mask;
}
EXPORT_SYMBOL_GPL(kvm_mmu_set_mmio_spte_mask);
static bool is_mmio_spte(u64 spte)
{
return (spte & shadow_mmio_mask) == shadow_mmio_value;
}
static inline bool sp_ad_disabled(struct kvm_mmu_page *sp)
{
return sp->role.ad_disabled;
}
static inline bool kvm_vcpu_ad_need_write_protect(struct kvm_vcpu *vcpu)
{
/*
* When using the EPT page-modification log, the GPAs in the log
* would come from L2 rather than L1. Therefore, we need to rely
* on write protection to record dirty pages. This also bypasses
* PML, since writes now result in a vmexit.
*/
return vcpu->arch.mmu == &vcpu->arch.guest_mmu;
}
static inline bool spte_ad_enabled(u64 spte)
{
MMU_WARN_ON(is_mmio_spte(spte));
return (spte & SPTE_SPECIAL_MASK) != SPTE_AD_DISABLED_MASK;
}
static inline bool spte_ad_need_write_protect(u64 spte)
{
MMU_WARN_ON(is_mmio_spte(spte));
return (spte & SPTE_SPECIAL_MASK) != SPTE_AD_ENABLED_MASK;
}
static bool is_nx_huge_page_enabled(void)
{
return READ_ONCE(nx_huge_pages);
}
static inline u64 spte_shadow_accessed_mask(u64 spte)
{
MMU_WARN_ON(is_mmio_spte(spte));
return spte_ad_enabled(spte) ? shadow_accessed_mask : 0;
}
static inline u64 spte_shadow_dirty_mask(u64 spte)
{
MMU_WARN_ON(is_mmio_spte(spte));
return spte_ad_enabled(spte) ? shadow_dirty_mask : 0;
}
static inline bool is_access_track_spte(u64 spte)
{
return !spte_ad_enabled(spte) && (spte & shadow_acc_track_mask) == 0;
}
/*
* Due to limited space in PTEs, the MMIO generation is a 19 bit subset of
* the memslots generation and is derived as follows:
*
* Bits 0-8 of the MMIO generation are propagated to spte bits 3-11
* Bits 9-18 of the MMIO generation are propagated to spte bits 52-61
*
* The KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS flag is intentionally not included in
* the MMIO generation number, as doing so would require stealing a bit from
* the "real" generation number and thus effectively halve the maximum number
* of MMIO generations that can be handled before encountering a wrap (which
* requires a full MMU zap). The flag is instead explicitly queried when
* checking for MMIO spte cache hits.
*/
#define MMIO_SPTE_GEN_MASK GENMASK_ULL(17, 0)
#define MMIO_SPTE_GEN_LOW_START 3
#define MMIO_SPTE_GEN_LOW_END 11
#define MMIO_SPTE_GEN_LOW_MASK GENMASK_ULL(MMIO_SPTE_GEN_LOW_END, \
MMIO_SPTE_GEN_LOW_START)
#define MMIO_SPTE_GEN_HIGH_START PT64_SECOND_AVAIL_BITS_SHIFT
#define MMIO_SPTE_GEN_HIGH_END 62
#define MMIO_SPTE_GEN_HIGH_MASK GENMASK_ULL(MMIO_SPTE_GEN_HIGH_END, \
MMIO_SPTE_GEN_HIGH_START)
static u64 generation_mmio_spte_mask(u64 gen)
{
u64 mask;
WARN_ON(gen & ~MMIO_SPTE_GEN_MASK);
BUILD_BUG_ON((MMIO_SPTE_GEN_HIGH_MASK | MMIO_SPTE_GEN_LOW_MASK) & SPTE_SPECIAL_MASK);
mask = (gen << MMIO_SPTE_GEN_LOW_START) & MMIO_SPTE_GEN_LOW_MASK;
mask |= (gen << MMIO_SPTE_GEN_HIGH_START) & MMIO_SPTE_GEN_HIGH_MASK;
return mask;
}
static u64 get_mmio_spte_generation(u64 spte)
{
u64 gen;
gen = (spte & MMIO_SPTE_GEN_LOW_MASK) >> MMIO_SPTE_GEN_LOW_START;
gen |= (spte & MMIO_SPTE_GEN_HIGH_MASK) >> MMIO_SPTE_GEN_HIGH_START;
return gen;
}
static u64 make_mmio_spte(struct kvm_vcpu *vcpu, u64 gfn, unsigned int access)
{
u64 gen = kvm_vcpu_memslots(vcpu)->generation & MMIO_SPTE_GEN_MASK;
u64 mask = generation_mmio_spte_mask(gen);
u64 gpa = gfn << PAGE_SHIFT;
access &= shadow_mmio_access_mask;
mask |= shadow_mmio_value | access;
mask |= gpa | shadow_nonpresent_or_rsvd_mask;
mask |= (gpa & shadow_nonpresent_or_rsvd_mask)
<< shadow_nonpresent_or_rsvd_mask_len;
return mask;
}
static void mark_mmio_spte(struct kvm_vcpu *vcpu, u64 *sptep, u64 gfn,
unsigned int access)
{
u64 mask = make_mmio_spte(vcpu, gfn, access);
unsigned int gen = get_mmio_spte_generation(mask);
access = mask & ACC_ALL;
trace_mark_mmio_spte(sptep, gfn, access, gen);
mmu_spte_set(sptep, mask);
}
static gfn_t get_mmio_spte_gfn(u64 spte)
{
u64 gpa = spte & shadow_nonpresent_or_rsvd_lower_gfn_mask;
gpa |= (spte >> shadow_nonpresent_or_rsvd_mask_len)
& shadow_nonpresent_or_rsvd_mask;
return gpa >> PAGE_SHIFT;
}
static unsigned get_mmio_spte_access(u64 spte)
{
return spte & shadow_mmio_access_mask;
}
static bool set_mmio_spte(struct kvm_vcpu *vcpu, u64 *sptep, gfn_t gfn,
kvm_pfn_t pfn, unsigned int access)
{
if (unlikely(is_noslot_pfn(pfn))) {
mark_mmio_spte(vcpu, sptep, gfn, access);
return true;
}
return false;
}
static bool check_mmio_spte(struct kvm_vcpu *vcpu, u64 spte)
{
u64 kvm_gen, spte_gen, gen;
gen = kvm_vcpu_memslots(vcpu)->generation;
if (unlikely(gen & KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS))
return false;
kvm_gen = gen & MMIO_SPTE_GEN_MASK;
spte_gen = get_mmio_spte_generation(spte);
trace_check_mmio_spte(spte, kvm_gen, spte_gen);
return likely(kvm_gen == spte_gen);
}
/*
* Sets the shadow PTE masks used by the MMU.
*
* Assumptions:
* - Setting either @accessed_mask or @dirty_mask requires setting both
* - At least one of @accessed_mask or @acc_track_mask must be set
*/
void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask,
u64 dirty_mask, u64 nx_mask, u64 x_mask, u64 p_mask,
u64 acc_track_mask, u64 me_mask)
{
BUG_ON(!dirty_mask != !accessed_mask);
BUG_ON(!accessed_mask && !acc_track_mask);
BUG_ON(acc_track_mask & SPTE_SPECIAL_MASK);
shadow_user_mask = user_mask;
shadow_accessed_mask = accessed_mask;
shadow_dirty_mask = dirty_mask;
shadow_nx_mask = nx_mask;
shadow_x_mask = x_mask;
shadow_present_mask = p_mask;
shadow_acc_track_mask = acc_track_mask;
shadow_me_mask = me_mask;
}
EXPORT_SYMBOL_GPL(kvm_mmu_set_mask_ptes);
static u8 kvm_get_shadow_phys_bits(void)
{
/*
* boot_cpu_data.x86_phys_bits is reduced when MKTME or SME are detected
* in CPU detection code, but the processor treats those reduced bits as
* 'keyID' thus they are not reserved bits. Therefore KVM needs to look at
* the physical address bits reported by CPUID.
*/
if (likely(boot_cpu_data.extended_cpuid_level >= 0x80000008))
return cpuid_eax(0x80000008) & 0xff;
/*
* Quite weird to have VMX or SVM but not MAXPHYADDR; probably a VM with
* custom CPUID. Proceed with whatever the kernel found since these features
* aren't virtualizable (SME/SEV also require CPUIDs higher than 0x80000008).
*/
return boot_cpu_data.x86_phys_bits;
}
static void kvm_mmu_reset_all_pte_masks(void)
{
u8 low_phys_bits;
shadow_user_mask = 0;
shadow_accessed_mask = 0;
shadow_dirty_mask = 0;
shadow_nx_mask = 0;
shadow_x_mask = 0;
shadow_mmio_mask = 0;
shadow_present_mask = 0;
shadow_acc_track_mask = 0;
shadow_phys_bits = kvm_get_shadow_phys_bits();
/*
* If the CPU has 46 or less physical address bits, then set an
* appropriate mask to guard against L1TF attacks. Otherwise, it is
* assumed that the CPU is not vulnerable to L1TF.
*
* Some Intel CPUs address the L1 cache using more PA bits than are
* reported by CPUID. Use the PA width of the L1 cache when possible
* to achieve more effective mitigation, e.g. if system RAM overlaps
* the most significant bits of legal physical address space.
*/
shadow_nonpresent_or_rsvd_mask = 0;
low_phys_bits = boot_cpu_data.x86_cache_bits;
if (boot_cpu_data.x86_cache_bits <
52 - shadow_nonpresent_or_rsvd_mask_len) {
shadow_nonpresent_or_rsvd_mask =
rsvd_bits(boot_cpu_data.x86_cache_bits -
shadow_nonpresent_or_rsvd_mask_len,
boot_cpu_data.x86_cache_bits - 1);
low_phys_bits -= shadow_nonpresent_or_rsvd_mask_len;
} else
WARN_ON_ONCE(boot_cpu_has_bug(X86_BUG_L1TF));
shadow_nonpresent_or_rsvd_lower_gfn_mask =
GENMASK_ULL(low_phys_bits - 1, PAGE_SHIFT);
}
static int is_cpuid_PSE36(void)
{
return 1;
}
static int is_nx(struct kvm_vcpu *vcpu)
{
return vcpu->arch.efer & EFER_NX;
}
static int is_shadow_present_pte(u64 pte)
{
return (pte != 0) && !is_mmio_spte(pte);
}
static int is_large_pte(u64 pte)
{
return pte & PT_PAGE_SIZE_MASK;
}
static int is_last_spte(u64 pte, int level)
{
if (level == PT_PAGE_TABLE_LEVEL)
return 1;
if (is_large_pte(pte))
return 1;
return 0;
}
static bool is_executable_pte(u64 spte)
{
return (spte & (shadow_x_mask | shadow_nx_mask)) == shadow_x_mask;
}
static kvm_pfn_t spte_to_pfn(u64 pte)
{
return (pte & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;
}
static gfn_t pse36_gfn_delta(u32 gpte)
{
int shift = 32 - PT32_DIR_PSE36_SHIFT - PAGE_SHIFT;
return (gpte & PT32_DIR_PSE36_MASK) << shift;
}
#ifdef CONFIG_X86_64
static void __set_spte(u64 *sptep, u64 spte)
{
WRITE_ONCE(*sptep, spte);
}
static void __update_clear_spte_fast(u64 *sptep, u64 spte)
{
WRITE_ONCE(*sptep, spte);
}
static u64 __update_clear_spte_slow(u64 *sptep, u64 spte)
{
return xchg(sptep, spte);
}
static u64 __get_spte_lockless(u64 *sptep)
{
return READ_ONCE(*sptep);
}
#else
union split_spte {
struct {
u32 spte_low;
u32 spte_high;
};
u64 spte;
};
static void count_spte_clear(u64 *sptep, u64 spte)
{
struct kvm_mmu_page *sp = page_header(__pa(sptep));
if (is_shadow_present_pte(spte))
return;
/* Ensure the spte is completely set before we increase the count */
smp_wmb();
sp->clear_spte_count++;
}
static void __set_spte(u64 *sptep, u64 spte)
{
union split_spte *ssptep, sspte;
ssptep = (union split_spte *)sptep;
sspte = (union split_spte)spte;
ssptep->spte_high = sspte.spte_high;
/*
* If we map the spte from nonpresent to present, We should store
* the high bits firstly, then set present bit, so cpu can not
* fetch this spte while we are setting the spte.
*/
smp_wmb();
WRITE_ONCE(ssptep->spte_low, sspte.spte_low);
}
static void __update_clear_spte_fast(u64 *sptep, u64 spte)
{
union split_spte *ssptep, sspte;
ssptep = (union split_spte *)sptep;
sspte = (union split_spte)spte;
WRITE_ONCE(ssptep->spte_low, sspte.spte_low);
/*
* If we map the spte from present to nonpresent, we should clear
* present bit firstly to avoid vcpu fetch the old high bits.
*/
smp_wmb();
ssptep->spte_high = sspte.spte_high;
count_spte_clear(sptep, spte);
}
static u64 __update_clear_spte_slow(u64 *sptep, u64 spte)
{
union split_spte *ssptep, sspte, orig;
ssptep = (union split_spte *)sptep;
sspte = (union split_spte)spte;
/* xchg acts as a barrier before the setting of the high bits */
orig.spte_low = xchg(&ssptep->spte_low, sspte.spte_low);
orig.spte_high = ssptep->spte_high;
ssptep->spte_high = sspte.spte_high;
count_spte_clear(sptep, spte);
return orig.spte;
}
/*
* The idea using the light way get the spte on x86_32 guest is from
* gup_get_pte (mm/gup.c).
*
* An spte tlb flush may be pending, because kvm_set_pte_rmapp
* coalesces them and we are running out of the MMU lock. Therefore
* we need to protect against in-progress updates of the spte.
*
* Reading the spte while an update is in progress may get the old value
* for the high part of the spte. The race is fine for a present->non-present
* change (because the high part of the spte is ignored for non-present spte),
* but for a present->present change we must reread the spte.
*
* All such changes are done in two steps (present->non-present and
* non-present->present), hence it is enough to count the number of
* present->non-present updates: if it changed while reading the spte,
* we might have hit the race. This is done using clear_spte_count.
*/
static u64 __get_spte_lockless(u64 *sptep)
{
struct kvm_mmu_page *sp = page_header(__pa(sptep));
union split_spte spte, *orig = (union split_spte *)sptep;
int count;
retry:
count = sp->clear_spte_count;
smp_rmb();
spte.spte_low = orig->spte_low;
smp_rmb();
spte.spte_high = orig->spte_high;
smp_rmb();
if (unlikely(spte.spte_low != orig->spte_low ||
count != sp->clear_spte_count))
goto retry;
return spte.spte;
}
#endif
static bool spte_can_locklessly_be_made_writable(u64 spte)
{
return (spte & (SPTE_HOST_WRITEABLE | SPTE_MMU_WRITEABLE)) ==
(SPTE_HOST_WRITEABLE | SPTE_MMU_WRITEABLE);
}
static bool spte_has_volatile_bits(u64 spte)
{
if (!is_shadow_present_pte(spte))
return false;
/*
* Always atomically update spte if it can be updated
* out of mmu-lock, it can ensure dirty bit is not lost,
* also, it can help us to get a stable is_writable_pte()
* to ensure tlb flush is not missed.
*/
if (spte_can_locklessly_be_made_writable(spte) ||
is_access_track_spte(spte))
return true;
if (spte_ad_enabled(spte)) {
if ((spte & shadow_accessed_mask) == 0 ||
(is_writable_pte(spte) && (spte & shadow_dirty_mask) == 0))
return true;
}
return false;
}
static bool is_accessed_spte(u64 spte)
{
u64 accessed_mask = spte_shadow_accessed_mask(spte);
return accessed_mask ? spte & accessed_mask
: !is_access_track_spte(spte);
}
static bool is_dirty_spte(u64 spte)
{
u64 dirty_mask = spte_shadow_dirty_mask(spte);
return dirty_mask ? spte & dirty_mask : spte & PT_WRITABLE_MASK;
}
/* Rules for using mmu_spte_set:
* Set the sptep from nonpresent to present.
* Note: the sptep being assigned *must* be either not present
* or in a state where the hardware will not attempt to update
* the spte.
*/
static void mmu_spte_set(u64 *sptep, u64 new_spte)
{
WARN_ON(is_shadow_present_pte(*sptep));
__set_spte(sptep, new_spte);
}
/*
* Update the SPTE (excluding the PFN), but do not track changes in its
* accessed/dirty status.
*/
static u64 mmu_spte_update_no_track(u64 *sptep, u64 new_spte)
{
u64 old_spte = *sptep;
WARN_ON(!is_shadow_present_pte(new_spte));
if (!is_shadow_present_pte(old_spte)) {
mmu_spte_set(sptep, new_spte);
return old_spte;
}
if (!spte_has_volatile_bits(old_spte))
__update_clear_spte_fast(sptep, new_spte);
else
old_spte = __update_clear_spte_slow(sptep, new_spte);
WARN_ON(spte_to_pfn(old_spte) != spte_to_pfn(new_spte));
return old_spte;
}
/* Rules for using mmu_spte_update:
* Update the state bits, it means the mapped pfn is not changed.
*
* Whenever we overwrite a writable spte with a read-only one we
* should flush remote TLBs. Otherwise rmap_write_protect
* will find a read-only spte, even though the writable spte
* might be cached on a CPU's TLB, the return value indicates this
* case.
*
* Returns true if the TLB needs to be flushed
*/
static bool mmu_spte_update(u64 *sptep, u64 new_spte)
{
bool flush = false;
u64 old_spte = mmu_spte_update_no_track(sptep, new_spte);
if (!is_shadow_present_pte(old_spte))
return false;
/*
* For the spte updated out of mmu-lock is safe, since
* we always atomically update it, see the comments in
* spte_has_volatile_bits().
*/
if (spte_can_locklessly_be_made_writable(old_spte) &&
!is_writable_pte(new_spte))
flush = true;
/*
* Flush TLB when accessed/dirty states are changed in the page tables,
* to guarantee consistency between TLB and page tables.
*/
if (is_accessed_spte(old_spte) && !is_accessed_spte(new_spte)) {
flush = true;
kvm_set_pfn_accessed(spte_to_pfn(old_spte));
}
if (is_dirty_spte(old_spte) && !is_dirty_spte(new_spte)) {
flush = true;
kvm_set_pfn_dirty(spte_to_pfn(old_spte));
}
return flush;
}
/*
* Rules for using mmu_spte_clear_track_bits:
* It sets the sptep from present to nonpresent, and track the
* state bits, it is used to clear the last level sptep.
* Returns non-zero if the PTE was previously valid.
*/
static int mmu_spte_clear_track_bits(u64 *sptep)
{
kvm_pfn_t pfn;
u64 old_spte = *sptep;
if (!spte_has_volatile_bits(old_spte))
__update_clear_spte_fast(sptep, 0ull);
else
old_spte = __update_clear_spte_slow(sptep, 0ull);
if (!is_shadow_present_pte(old_spte))
return 0;
pfn = spte_to_pfn(old_spte);
/*
* KVM does not hold the refcount of the page used by
* kvm mmu, before reclaiming the page, we should
* unmap it from mmu first.
*/
WARN_ON(!kvm_is_reserved_pfn(pfn) && !page_count(pfn_to_page(pfn)));
if (is_accessed_spte(old_spte))
kvm_set_pfn_accessed(pfn);
if (is_dirty_spte(old_spte))
kvm_set_pfn_dirty(pfn);
return 1;
}
/*
* Rules for using mmu_spte_clear_no_track:
* Directly clear spte without caring the state bits of sptep,
* it is used to set the upper level spte.
*/
static void mmu_spte_clear_no_track(u64 *sptep)
{
__update_clear_spte_fast(sptep, 0ull);
}
static u64 mmu_spte_get_lockless(u64 *sptep)
{
return __get_spte_lockless(sptep);
}
static u64 mark_spte_for_access_track(u64 spte)
{
if (spte_ad_enabled(spte))
return spte & ~shadow_accessed_mask;
if (is_access_track_spte(spte))
return spte;
/*
* Making an Access Tracking PTE will result in removal of write access
* from the PTE. So, verify that we will be able to restore the write
* access in the fast page fault path later on.
*/
WARN_ONCE((spte & PT_WRITABLE_MASK) &&
!spte_can_locklessly_be_made_writable(spte),
"kvm: Writable SPTE is not locklessly dirty-trackable\n");
WARN_ONCE(spte & (shadow_acc_track_saved_bits_mask <<
shadow_acc_track_saved_bits_shift),
"kvm: Access Tracking saved bit locations are not zero\n");
spte |= (spte & shadow_acc_track_saved_bits_mask) <<
shadow_acc_track_saved_bits_shift;
spte &= ~shadow_acc_track_mask;
return spte;
}
/* Restore an acc-track PTE back to a regular PTE */
static u64 restore_acc_track_spte(u64 spte)
{
u64 new_spte = spte;
u64 saved_bits = (spte >> shadow_acc_track_saved_bits_shift)
& shadow_acc_track_saved_bits_mask;
WARN_ON_ONCE(spte_ad_enabled(spte));
WARN_ON_ONCE(!is_access_track_spte(spte));