From 93984f19e7bce4c18084a6ef3dacafb155b806ed Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Fri, 29 Apr 2022 21:00:23 +0000 Subject: KVM: Fully serialize gfn=>pfn cache refresh via mutex 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 Signed-off-by: Sean Christopherson Message-Id: <20220429210025.3293691-7-seanjc@google.com> Signed-off-by: Paolo Bonzini --- virt/kvm/pfncache.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'virt/kvm') diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c index 05cb0bcbf662..f610d3945b69 100644 --- a/virt/kvm/pfncache.c +++ b/virt/kvm/pfncache.c @@ -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) 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); 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: write_unlock_irq(&gpc->lock); + mutex_unlock(&gpc->refresh_lock); + gpc_release_pfn_and_khva(kvm, old_pfn, old_khva); 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; kvm_pfn_t old_pfn; + mutex_lock(&gpc->refresh_lock); write_lock_irq(&gpc->lock); 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; write_unlock_irq(&gpc->lock); + mutex_unlock(&gpc->refresh_lock); 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) { rwlock_init(&gpc->lock); + mutex_init(&gpc->refresh_lock); gpc->khva = NULL; gpc->pfn = KVM_PFN_ERR_FAULT; -- cgit v1.2.3