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kernel/arm64: unconditionally set PTE shareability
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to Inner Shareable.

We noticed a lot of instability with the Jetson Orin port when running
in UP + HYP mode. Setting the shareability to Inner Shareable (IS)
unconditionally is the fix, however, we're unable to find the exact line
in Arm documentation that explains why this is the case.

Potential theory: there are other agents on the Jetson Orin that require
coherency and live in the IS domain. Being more permissive with
memory resolves the prefetching and translation faults we were getting.

For reference, Arm states "Arm expects operating systems to mark the
majority of DRAM memory as Normal Write-back cacheable, Inner
shareable" (102376_0200_01_en version 2).

Signed-off-by: Andy Bui <andy.bui@nio.io>
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Andy Bui committed Feb 8, 2024
1 parent ce8191c commit 67c4803
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Showing 2 changed files with 26 additions and 21 deletions.
37 changes: 21 additions & 16 deletions src/arch/arm/64/kernel/vspace.c
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Original file line number Diff line number Diff line change
Expand Up @@ -68,12 +68,20 @@ enum mair_s2_types {
S2_NORMAL = S2_NORMAL_INNER_WBC_OUTER_WBC
};

/* Leif from Linaro said the big.LITTLE clusters should be treated as
* inner shareable, and we believe so, although the Example B2-1 given in
* ARM ARM DDI 0487B.b (ID092517) says otherwise.
/* ARM DDI 0487J.a, section D8.5.2 */
/* Linux will only run on cores within the same Inner Shareable domain.
* They make an assumption that all the PEs are under a single IS domain,
* and we do the same here.
*
* Arm also states "Arm expects operating systems to mark the
* majority of DRAM memory as Normal Write-back cacheable, Inner
* shareable" (102376_0200_01_en version 2).
*
* Note: accoding to RPYFVQ (ARM ARM DDI 0487J.a), the shareability
* attribute for Device memory does not matter as it will instead
* be treated as Outer Shareable.
*/

#define SMP_SHARE 3
#define INNER_SHAREABLE 3

struct lookupPTSlot_ret {
pte_t *ptSlot;
Expand Down Expand Up @@ -184,13 +192,13 @@ BOOT_CODE void map_kernel_frame(paddr_t paddr, pptr_t vaddr, vm_rights_t vm_righ
word_t uxn = 1; /* unprivileged execute never */
#endif /* CONFIG_ARM_HYPERVISOR_SUPPORT */
word_t attr_index;
word_t shareable;

/* ARM ARM RPYFVQ: device memory is treated as Outer Shareable, and the PTE attribute has no effect. */
word_t shareable = INNER_SHAREABLE;
if (vm_attributes_get_armPageCacheable(attributes)) {
attr_index = NORMAL;
shareable = SMP_TERNARY(SMP_SHARE, 0);
} else {
attr_index = DEVICE_nGnRnE;
shareable = 0;
}
armKSGlobalKernelPT[GET_KPT_INDEX(vaddr, KLVL_FRM_ARM_PT_LVL(3))] = pte_pte_4k_page_new(uxn, paddr,
0, /* global */
Expand Down Expand Up @@ -244,7 +252,7 @@ BOOT_CODE void map_kernel_window(void)
paddr,
0, /* global */
1, /* access flag */
SMP_TERNARY(SMP_SHARE, 0), /* Inner-shareable if SMP enabled, otherwise unshared */
INNER_SHAREABLE,
0, /* VMKernelOnly */
NORMAL
);
Expand Down Expand Up @@ -303,7 +311,7 @@ static BOOT_CODE void map_it_frame_cap(cap_t vspace_cap, cap_t frame_cap, bool_t
1, /* not global */
#endif
1, /* access flag */
SMP_TERNARY(SMP_SHARE, 0), /* Inner-shareable if SMP enabled, otherwise unshared */
INNER_SHAREABLE,
APFromVMRights(VMReadWrite),
#ifdef CONFIG_ARM_HYPERVISOR_SUPPORT
S2_NORMAL
Expand Down Expand Up @@ -665,15 +673,12 @@ static pte_t makeUserPagePTE(paddr_t paddr, vm_rights_t vm_rights, vm_attributes
word_t attridx = cacheable ? NORMAL : DEVICE_nGnRnE;
#endif

/* Inner-shareable if SMP enabled, otherwise unshared (ignored for devices) */
word_t shareable = cacheable ? SMP_TERNARY(SMP_SHARE, 0) : 0;

if (page_size == ARMSmallPage) {
return pte_pte_4k_page_new(nonexecutable, paddr, nG, 1 /* access flag */,
shareable, APFromVMRights(vm_rights), attridx);
INNER_SHAREABLE, APFromVMRights(vm_rights), attridx);
} else {
return pte_pte_page_new(nonexecutable, paddr, nG, 1 /* access flag */,
shareable, APFromVMRights(vm_rights), attridx);
INNER_SHAREABLE, APFromVMRights(vm_rights), attridx);
}
}

Expand Down Expand Up @@ -1927,7 +1932,7 @@ exception_t benchmark_arch_map_logBuffer(word_t frame_cptr)
ksUserLogBuffer,
0, /* global */
1, /* access flag */
SMP_TERNARY(SMP_SHARE, 0), /* Inner-shareable if SMP enabled, otherwise unshared */
INNER_SHAREABLE,
0, /* VMKernelOnly */
NORMAL_WT);

Expand Down
10 changes: 5 additions & 5 deletions src/arch/arm/64/machine/capdl.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -21,7 +21,7 @@ word_t get_tcb_sp(tcb_t *tcb)

static void obj_frame_print_attrs(vm_page_size_t frameSize, paddr_t frameBase);
static void cap_frame_print_attrs_pt(pte_t *ptSlot);
static void cap_frame_print_attrs_impl(word_t SH, word_t AP, word_t NXN);
static void cap_frame_print_attrs_impl(word_t AttrIndx, word_t AP, word_t NXN);
static void cap_frame_print_attrs_vptr(word_t vptr, cap_t vspace);

static void _cap_frame_print_attrs_vptr(word_t vptr, vspace_root_t *vspaceRoot);
Expand Down Expand Up @@ -55,12 +55,12 @@ static void arm64_cap_pud_print_slots(void *pgdSlot_or_vspace, vptr_t vptr);
/* use when only have access to pte of frames */
static void cap_frame_print_attrs_pt(pte_t *ptSlot)
{
cap_frame_print_attrs_impl(pte_pte_page_ptr_get_SH(ptSlot),
cap_frame_print_attrs_impl(pte_pte_page_ptr_get_AttrIndx(ptSlot),
pte_pte_page_ptr_get_AP(ptSlot),
pte_pte_page_ptr_get_UXN(ptSlot));
}

static void cap_frame_print_attrs_impl(word_t SH, word_t AP, word_t NXN)
static void cap_frame_print_attrs_impl(word_t AttrIndx, word_t AP, word_t NXN)
{
printf("(");

Expand Down Expand Up @@ -96,8 +96,8 @@ static void cap_frame_print_attrs_impl(word_t SH, word_t AP, word_t NXN)
printf("X");
}

/* Only has effect if SMP enabled */
if (SH != SMP_TERNARY(SMP_SHARE, 0)) {
/* DEVICE_nGnRnE is the only attribute we use for uncached memory right now. */
if (AttrIndx == DEVICE_nGnRnE) {
printf(", uncached");
}

Expand Down

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