From 2e2409afe5f0c284c7dfe5504058e8d115806a7d Mon Sep 17 00:00:00 2001 From: Tom Lendacky Date: Fri, 20 Mar 2020 11:07:07 -0500 Subject: [PATCH] KVM: SVM: Issue WBINVD after deactivating an SEV guest Currently, CLFLUSH is used to flush SEV guest memory before the guest is terminated (or a memory hotplug region is removed). However, CLFLUSH is not enough to ensure that SEV guest tagged data is flushed from the cache. With 33af3a7ef9e6 ("KVM: SVM: Reduce WBINVD/DF_FLUSH invocations"), the original WBINVD was removed. This then exposed crashes at random times because of a cache flush race with a page that had both a hypervisor and a guest tag in the cache. Restore the WBINVD when destroying an SEV guest and add a WBINVD to the svm_unregister_enc_region() function to ensure hotplug memory is flushed when removed. The DF_FLUSH can still be avoided at this point. Fixes: 33af3a7ef9e6 ("KVM: SVM: Reduce WBINVD/DF_FLUSH invocations") Signed-off-by: Tom Lendacky Message-Id: Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini --- arch/x86/kvm/svm.c | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-) diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index f0aa9ff9666fe0..50d1ebafe0b31f 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -1933,14 +1933,6 @@ static void sev_clflush_pages(struct page *pages[], unsigned long npages) static void __unregister_enc_region_locked(struct kvm *kvm, struct enc_region *region) { - /* - * The guest may change the memory encryption attribute from C=0 -> C=1 - * or vice versa for this memory range. Lets make sure caches are - * flushed to ensure that guest data gets written into memory with - * correct C-bit. - */ - sev_clflush_pages(region->pages, region->npages); - sev_unpin_memory(kvm, region->pages, region->npages); list_del(®ion->list); kfree(region); @@ -1970,6 +1962,13 @@ static void sev_vm_destroy(struct kvm *kvm) mutex_lock(&kvm->lock); + /* + * Ensure that all guest tagged cache entries are flushed before + * releasing the pages back to the system for use. CLFLUSH will + * not do this, so issue a WBINVD. + */ + wbinvd_on_all_cpus(); + /* * if userspace was terminated before unregistering the memory regions * then lets unpin all the registered memory. @@ -7288,6 +7287,13 @@ static int svm_unregister_enc_region(struct kvm *kvm, goto failed; } + /* + * Ensure that all guest tagged cache entries are flushed before + * releasing the pages back to the system for use. CLFLUSH will + * not do this, so issue a WBINVD. + */ + wbinvd_on_all_cpus(); + __unregister_enc_region_locked(kvm, region); mutex_unlock(&kvm->lock);