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authorTom Lendacky <thomas.lendacky@amd.com>2020-03-20 11:07:07 -0500
committerPaolo Bonzini <pbonzini@redhat.com>2020-03-23 09:01:04 -0400
commit2e2409afe5f0c284c7dfe5504058e8d115806a7d (patch)
treee1937efd10e18ce5c6d3d32142eeb40f359e4ea2 /arch/x86
parent2da1ed62d55c6cbebbdee924f6af4e87bb6666e5 (diff)
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 <thomas.lendacky@amd.com> Message-Id: <c8bf9087ca3711c5770bdeaafa3e45b717dc5ef4.1584720426.git.thomas.lendacky@amd.com> Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/kvm/svm.c22
1 files changed, 14 insertions, 8 deletions
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index f0aa9ff9666f..50d1ebafe0b3 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(&region->list);
kfree(region);
@@ -1971,6 +1963,13 @@ 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);