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From:   Krish Sadhukhan <krish.sadhukhan@oracle.com>
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Subject: [PATCH 3/4 v3] x86: AMD: Don't flush cache if hardware enforces cache coherency across encryption domnains
Date:   Fri, 11 Sep 2020 19:26:00 +0000
Message-Id: <20200911192601.9591-4-krish.sadhukhan@oracle.com>
In-Reply-To: <20200911192601.9591-1-krish.sadhukhan@oracle.com>
References: <20200911192601.9591-1-krish.sadhukhan@oracle.com>
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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.

Suggested-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
---
 arch/x86/mm/pat/set_memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index d1b2a889f035..78d5511c5edd 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -1999,7 +1999,7 @@ static int __set_memory_enc_dec(unsigned long addr, int numpages, bool enc)
 	/*
 	 * Before changing the encryption attribute, we need to flush caches.
 	 */
-	cpa_flush(&cpa, 1);
+	cpa_flush(&cpa, !this_cpu_has(X86_FEATURE_HW_CACHE_COHERENCY));
 
 	ret = __change_page_attr_set_clr(&cpa, 1);
 
-- 
2.18.4