From: Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx> commit e1ebb2b49048c4767cfa0d8466f9c701e549fa5e upstream. In some hardware implementations, coherency between the encrypted and unencrypted mappings of the same physical page in a VM is enforced. In such a system, it is not required for software to flush the VM's page from all CPU caches in the system prior to changing the value of the C-bit for the page. So check that bit before flushing the cache. Signed-off-by: Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Link: https://lkml.kernel.org/r/20200917212038.5090-4-krish.sadhukhan@xxxxxxxxxx Signed-off-by: Liam Merwick <liam.merwick@xxxxxxxxxx> Conflicts: arch/x86/kvm/svm/sev.c [ The linux-5.4.y stable branch does not have the Linux 5.7 refactoring commit eaf78265a4ab ("KVM: SVM: Move SEV code to separate file") so the change was manually applied to sev_clflush_pages() in arch/x86/kvm/svm.c. ] --- arch/x86/kvm/svm.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index 2f84509f2828..125970286f28 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -1904,7 +1904,8 @@ static void sev_clflush_pages(struct page *pages[], unsigned long npages) uint8_t *page_virtual; unsigned long i; - if (npages == 0 || pages == NULL) + if (this_cpu_has(X86_FEATURE_SME_COHERENT) || npages == 0 || + pages == NULL) return; for (i = 0; i < npages; i++) { -- 2.27.0
