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KVM: Fully serialize gfn=>pfn cache refresh via mutex

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Protect gfn=>pfn cache refresh with a mutex to fully serialize refreshes.
The refresh logic doesn't protect against

- concurrent unmaps, or refreshes with different GPAs (which may or may not
  happen in practice, for example if a cache is only used under vcpu->mutex;
  but it's allowed in the code)

- a false negative on the memslot generation.  If the first refresh sees
  a stale memslot generation, it will refresh the hva and generation before
  moving on to the hva=>pfn translation.  If it then drops gpc->lock, a
  different user of the cache can come along, acquire gpc->lock, see that
  the memslot generation is fresh, and skip the hva=>pfn update due to the
  userspace address also matching (because it too was updated).

The refresh path can already sleep during hva=>pfn resolution, so wrap
the refresh with a mutex to ensure that any given refresh runs to
completion before other callers can start their refresh.

Cc: stable@vger.kernel.org
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220429210025.3293691-7-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2022-04-29 21:00:23 +00:00 committed by Paolo Bonzini
parent 3ba2c95ea1
commit 93984f19e7
2 changed files with 14 additions and 0 deletions
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2
include/linux/kvm_types.h
View File

@ -19,6 +19,7 @@ struct kvm_memslots;
enum kvm_mr_change; enum kvm_mr_change;
#include <linux/bits.h> #include <linux/bits.h>
#include <linux/mutex.h>
#include <linux/types.h> #include <linux/types.h>
#include <linux/spinlock_types.h> #include <linux/spinlock_types.h>
@ -69,6 +70,7 @@ struct gfn_to_pfn_cache {
struct kvm_vcpu *vcpu; struct kvm_vcpu *vcpu;
struct list_head list; struct list_head list;
rwlock_t lock; rwlock_t lock;
struct mutex refresh_lock;
void *khva; void *khva;
kvm_pfn_t pfn; kvm_pfn_t pfn;
enum pfn_cache_usage usage; enum pfn_cache_usage usage;

12
virt/kvm/pfncache.c
View File

@ -157,6 +157,13 @@ int kvm_gfn_to_pfn_cache_refresh(struct kvm *kvm, struct gfn_to_pfn_cache *gpc,
if (page_offset + len > PAGE_SIZE) if (page_offset + len > PAGE_SIZE)
return -EINVAL; return -EINVAL;
/*
* If another task is refreshing the cache, wait for it to complete.
* There is no guarantee that concurrent refreshes will see the same
* gpa, memslots generation, etc..., so they must be fully serialized.
*/
mutex_lock(&gpc->refresh_lock);
write_lock_irq(&gpc->lock); write_lock_irq(&gpc->lock);
old_pfn = gpc->pfn; old_pfn = gpc->pfn;
@ -248,6 +255,8 @@ int kvm_gfn_to_pfn_cache_refresh(struct kvm *kvm, struct gfn_to_pfn_cache *gpc,
out: out:
write_unlock_irq(&gpc->lock); write_unlock_irq(&gpc->lock);
mutex_unlock(&gpc->refresh_lock);
gpc_release_pfn_and_khva(kvm, old_pfn, old_khva); gpc_release_pfn_and_khva(kvm, old_pfn, old_khva);
return ret; return ret;
@ -259,6 +268,7 @@ void kvm_gfn_to_pfn_cache_unmap(struct kvm *kvm, struct gfn_to_pfn_cache *gpc)
void *old_khva; void *old_khva;
kvm_pfn_t old_pfn; kvm_pfn_t old_pfn;
mutex_lock(&gpc->refresh_lock);
write_lock_irq(&gpc->lock); write_lock_irq(&gpc->lock);
gpc->valid = false; gpc->valid = false;
@ -274,6 +284,7 @@ void kvm_gfn_to_pfn_cache_unmap(struct kvm *kvm, struct gfn_to_pfn_cache *gpc)
gpc->pfn = KVM_PFN_ERR_FAULT; gpc->pfn = KVM_PFN_ERR_FAULT;
write_unlock_irq(&gpc->lock); write_unlock_irq(&gpc->lock);
mutex_unlock(&gpc->refresh_lock);
gpc_release_pfn_and_khva(kvm, old_pfn, old_khva); gpc_release_pfn_and_khva(kvm, old_pfn, old_khva);
} }
@ -288,6 +299,7 @@ int kvm_gfn_to_pfn_cache_init(struct kvm *kvm, struct gfn_to_pfn_cache *gpc,
if (!gpc->active) { if (!gpc->active) {
rwlock_init(&gpc->lock); rwlock_init(&gpc->lock);
mutex_init(&gpc->refresh_lock);
gpc->khva = NULL; gpc->khva = NULL;
gpc->pfn = KVM_PFN_ERR_FAULT; gpc->pfn = KVM_PFN_ERR_FAULT;