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KVM: pfncache: allow a cache to be activated with a fixed (userspace)…
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… HVA

Some pfncache pages may actually be overlays on guest memory that have a
fixed HVA within the VMM. It's pointless to invalidate such cached
mappings if the overlay is moved so allow a cache to be activated directly
with the HVA to cater for such cases. A subsequent patch will make use
of this facility.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/20240215152916.1158-10-paul@xen.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
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@sean-jc
Paul Durrant authored and sean-jc committed Feb 20, 2024
1 parent 9e7325a commit 721f5b0
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Showing 2 changed files with 101 additions and 28 deletions.
31 changes: 31 additions & 0 deletions include/linux/kvm_host.h
View file
Expand Up @@ -148,6 +148,11 @@ static inline bool kvm_is_error_hva(unsigned long addr)

#endif

static inline bool kvm_is_error_gpa(gpa_t gpa)
{
return gpa == INVALID_GPA;
}

#define KVM_ERR_PTR_BAD_PAGE (ERR_PTR(-ENOENT))

static inline bool is_error_page(struct page *page)
Expand Down Expand Up @@ -1344,6 +1349,22 @@ void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm);
*/
int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len);

/**
* kvm_gpc_activate_hva - prepare a cached kernel mapping and HPA for a given HVA.
*
* @gpc: struct gfn_to_pfn_cache object.
* @hva: userspace virtual address to map.
* @len: sanity check; the range being access must fit a single page.
*
* @return: 0 for success.
* -EINVAL for a mapping which would cross a page boundary.
* -EFAULT for an untranslatable guest physical address.
*
* The semantics of this function are the same as those of kvm_gpc_activate(). It
* merely bypasses a layer of address translation.
*/
int kvm_gpc_activate_hva(struct gfn_to_pfn_cache *gpc, unsigned long hva, unsigned long len);

/**
* kvm_gpc_check - check validity of a gfn_to_pfn_cache.
*
Expand Down Expand Up @@ -1390,6 +1411,16 @@ int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len);
*/
void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc);

static inline bool kvm_gpc_is_gpa_active(struct gfn_to_pfn_cache *gpc)
{
return gpc->active && !kvm_is_error_gpa(gpc->gpa);
}

static inline bool kvm_gpc_is_hva_active(struct gfn_to_pfn_cache *gpc)
{
return gpc->active && kvm_is_error_gpa(gpc->gpa);
}

void kvm_sigset_activate(struct kvm_vcpu *vcpu);
void kvm_sigset_deactivate(struct kvm_vcpu *vcpu);

Expand Down
98 changes: 70 additions & 28 deletions virt/kvm/pfncache.c
View file
Expand Up @@ -48,7 +48,14 @@ bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, unsigned long len)
if (!gpc->active)
return false;

if (gpc->generation != slots->generation || kvm_is_error_hva(gpc->uhva))
/*
* If the page was cached from a memslot, make sure the memslots have
* not been re-configured.
*/
if (!kvm_is_error_gpa(gpc->gpa) && gpc->generation != slots->generation)
return false;

if (kvm_is_error_hva(gpc->uhva))
return false;

if (offset_in_page(gpc->uhva) + len > PAGE_SIZE)
Expand Down Expand Up @@ -209,22 +216,27 @@ static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
return -EFAULT;
}

static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long uhva,
unsigned long len)
{
struct kvm_memslots *slots = kvm_memslots(gpc->kvm);
unsigned long page_offset = offset_in_page(gpa);
unsigned long page_offset;
bool unmap_old = false;
unsigned long old_uhva;
kvm_pfn_t old_pfn;
bool hva_change = false;
void *old_khva;
int ret;

/* Either gpa or uhva must be valid, but not both */
if (WARN_ON_ONCE(kvm_is_error_gpa(gpa) == kvm_is_error_hva(uhva)))
return -EINVAL;

/*
* If must fit within a single page. The 'len' argument is
* only to enforce that.
* The cached acces must fit within a single page. The 'len' argument
* exists only to enforce that.
*/
page_offset = kvm_is_error_gpa(gpa) ? offset_in_page(uhva) :
offset_in_page(gpa);
if (page_offset + len > PAGE_SIZE)
return -EINVAL;

Expand All @@ -246,29 +258,39 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
old_khva = (void *)PAGE_ALIGN_DOWN((uintptr_t)gpc->khva);
old_uhva = PAGE_ALIGN_DOWN(gpc->uhva);

/* Refresh the userspace HVA if necessary */
if (gpc->gpa != gpa || gpc->generation != slots->generation ||
kvm_is_error_hva(gpc->uhva)) {
gfn_t gfn = gpa_to_gfn(gpa);

gpc->gpa = gpa;
gpc->generation = slots->generation;
gpc->memslot = __gfn_to_memslot(slots, gfn);
gpc->uhva = gfn_to_hva_memslot(gpc->memslot, gfn);
if (kvm_is_error_gpa(gpa)) {
gpc->gpa = INVALID_GPA;
gpc->memslot = NULL;
gpc->uhva = PAGE_ALIGN_DOWN(uhva);

if (kvm_is_error_hva(gpc->uhva)) {
ret = -EFAULT;
goto out;
}

/*
* Even if the GPA and/or the memslot generation changed, the
* HVA may still be the same.
*/
if (gpc->uhva != old_uhva)
hva_change = true;
} else {
gpc->uhva = old_uhva;
struct kvm_memslots *slots = kvm_memslots(gpc->kvm);

if (gpc->gpa != gpa || gpc->generation != slots->generation ||
kvm_is_error_hva(gpc->uhva)) {
gfn_t gfn = gpa_to_gfn(gpa);

gpc->gpa = gpa;
gpc->generation = slots->generation;
gpc->memslot = __gfn_to_memslot(slots, gfn);
gpc->uhva = gfn_to_hva_memslot(gpc->memslot, gfn);

if (kvm_is_error_hva(gpc->uhva)) {
ret = -EFAULT;
goto out;
}

/*
* Even if the GPA and/or the memslot generation changed, the
* HVA may still be the same.
*/
if (gpc->uhva != old_uhva)
hva_change = true;
} else {
gpc->uhva = old_uhva;
}
}

/* Note: the offset must be correct before calling hva_to_pfn_retry() */
Expand Down Expand Up @@ -319,7 +341,15 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,

int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len)
{
return __kvm_gpc_refresh(gpc, gpc->gpa, len);
/*
* If the GPA is valid then ignore the HVA, as a cache can be GPA-based
* or HVA-based, not both. For GPA-based caches, the HVA will be
* recomputed during refresh if necessary.
*/
unsigned long uhva = kvm_is_error_gpa(gpc->gpa) ? gpc->uhva :
KVM_HVA_ERR_BAD;

return __kvm_gpc_refresh(gpc, gpc->gpa, uhva, len);
}

void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm)
Expand All @@ -329,10 +359,12 @@ void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm)

gpc->kvm = kvm;
gpc->pfn = KVM_PFN_ERR_FAULT;
gpc->gpa = INVALID_GPA;
gpc->uhva = KVM_HVA_ERR_BAD;
}

int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
static int __kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long uhva,
unsigned long len)
{
struct kvm *kvm = gpc->kvm;

Expand All @@ -353,7 +385,17 @@ int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
gpc->active = true;
write_unlock_irq(&gpc->lock);
}
return __kvm_gpc_refresh(gpc, gpa, len);
return __kvm_gpc_refresh(gpc, gpa, uhva, len);
}

int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
{
return __kvm_gpc_activate(gpc, gpa, KVM_HVA_ERR_BAD, len);
}

int kvm_gpc_activate_hva(struct gfn_to_pfn_cache *gpc, unsigned long uhva, unsigned long len)
{
return __kvm_gpc_activate(gpc, INVALID_GPA, uhva, len);
}

void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc)
Expand Down

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