From: Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx> commit 75d1cc0e05af579301ce4e49cf6399be4b4e6e76 upstream. In some hardware implementations, coherency between the encrypted and unencrypted mappings of the same physical page is enforced. In such a system, it is not required for software to flush the 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. [ bp: Massage commit message. ] Suggested-by: Tom Lendacky <thomas.lendacky@xxxxxxx> Signed-off-by: Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Link: https://lkml.kernel.org/r/20200917212038.5090-3-krish.sadhukhan@xxxxxxxxxx Signed-off-by: Liam Merwick <liam.merwick@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/mm/pageattr.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/arch/x86/mm/pageattr.c +++ b/arch/x86/mm/pageattr.c @@ -1967,7 +1967,7 @@ static int __set_memory_enc_dec(unsigned /* * Before changing the encryption attribute, we need to flush caches. */ - cpa_flush(&cpa, 1); + cpa_flush(&cpa, !this_cpu_has(X86_FEATURE_SME_COHERENT)); ret = __change_page_attr_set_clr(&cpa, 1);
