linux-kernel - [PATCH 5.4 42/43] x86/mm/pat: Dont flush cache if hardware enforces cache coherency across encryption domnains

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Date:   Mon, 14 Mar 2022 12:53:53 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Tom Lendacky <thomas.lendacky@....com>,
        Krish Sadhukhan <krish.sadhukhan@...cle.com>,
        Borislav Petkov <bp@...e.de>,
        Liam Merwick <liam.merwick@...cle.com>
Subject: [PATCH 5.4 42/43] x86/mm/pat: Dont flush cache if hardware enforces cache coherency across encryption domnains

From: Krish Sadhukhan <krish.sadhukhan@...cle.com>

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@....com>
Signed-off-by: Krish Sadhukhan <krish.sadhukhan@...cle.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Link: https://lkml.kernel.org/r/20200917212038.5090-3-krish.sadhukhan@oracle.com
Signed-off-by: Liam Merwick <liam.merwick@...cle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 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);