[PATCH v13 09/21] KVM: pfncache: allow a cache to be activated with a fixed (userspace) HVA

Paul Durrant
2024-02-15T15:30:52Z

From: Paul Durrant <pdurrant@amazon.com>

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>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>

v13:
- Define kvm_is_error_gpa() to check GPA validity.
- Add an either/or address check to __kvm_gpc_refresh() as requested.
- Make sure memslot is NULL if the cache is activated with an HVA.

v11:
- Fixed kvm_gpc_check() to ignore memslot generation if the cache is not
activated with a GPA. (This breakage occured during the re-work for v8).

v9:
- Pass both GPA and HVA into __kvm_gpc_refresh() rather than overloading
the address paraneter and using a bool flag to indicated what it is.

v8:
- Re-worked to avoid messing with struct gfn_to_pfn_cache.
---
include/linux/kvm_host.h | 21 +++++++++
virt/kvm/pfncache.c | 94 +++++++++++++++++++++++++++++-----------
2 files changed, 89 insertions(+), 26 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 41ee515b304e..043cc824d55a 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -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)
@@ -1343,6 +1348,22 @@ 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.
*
diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index 97eec8ee3449..4e64d349b2f7 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -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)
@@ -209,11 +216,11 @@ 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 = kvm_is_error_gpa(gpa) ?
+ offset_in_page(uhva) : offset_in_page(gpa);
bool unmap_old = false;
unsigned long old_uhva;
kvm_pfn_t old_pfn;
@@ -221,6 +228,10 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
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.
@@ -246,29 +257,39 @@ 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() */
@@ -319,7 +340,16 @@ 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);
+ unsigned long uhva = gpc->uhva;
+
+ /*
+ * If the GPA is valid then invalidate the HVA, otherwise
+ * __kvm_gpc_refresh() will fail its strict either/or address check.
+ */
+ if (!kvm_is_error_gpa(gpc->gpa))
+ 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)
@@ -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;

@@ -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)
--
2.39.2