linux-kernel - [PATCH] x86/sev-es: Do not unroll string I/O for SEV-ES guests

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Date:   Mon,  1 Feb 2021 12:26:27 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>, Joerg Roedel <jroedel@...e.de>
Subject: [PATCH] x86/sev-es: Do not unroll string I/O for SEV-ES guests

From: Tom Lendacky <thomas.lendacky@....com>

Under the GHCB specification, SEV-ES guests can support string I/O. The
current #VC handler contains this support, so remove the need to unroll
kernel string I/O operations. This will reduce the number of #VC
exceptions generated as well as the number VMEXITS for the guest.

Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
---
 arch/x86/mm/mem_encrypt.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index c79e5736ab2b..d55ea77e1ca8 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -474,9 +474,10 @@ void __init mem_encrypt_init(void)
 	swiotlb_update_mem_attributes();
 
 	/*
-	 * With SEV, we need to unroll the rep string I/O instructions.
+	 * With SEV, we need to unroll the rep string I/O instructions,
+	 * but SEV-ES supports them through the #VC handler.
 	 */
-	if (sev_active())
+	if (sev_active() && !sev_es_active())
 		static_branch_enable(&sev_enable_key);
 
 	print_mem_encrypt_feature_info();

base-commit: a7e0bdf1b07ea6169930ec42b0bdb17e1c1e3bb0
-- 
2.30.0