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Subject[PATCH 3/4 v3] x86: AMD: Don't flush cache if hardware enforces cache coherency across encryption domnains
Date
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
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