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Commit afb684cb authored by Krish Sadhukhan's avatar Krish Sadhukhan Committed by Greg Kroah-Hartman
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KVM: SVM: Don't flush cache if hardware enforces cache coherency across encryption domains 



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: default avatarKrish Sadhukhan <krish.sadhukhan@oracle.com>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Acked-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Link: https://lkml.kernel.org/r/20200917212038.5090-4-krish.sadhukhan@oracle.com


[ 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. ]
Signed-off-by: default avatarLiam Merwick <liam.merwick@oracle.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 690909c6

arch/x86/kvm/svm.c

+2 −1
Original line number Diff line number Diff line
@@ -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++) {