linux-kernel - [PATCH] KVM: x86: clflushopt should be treated as a no-op by emulation

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Message-Id: <20201103120400.240882-1-david.edmondson@oracle.com>
Date:   Tue,  3 Nov 2020 12:04:00 +0000
From:   David Edmondson <david.edmondson@...cle.com>
To:     linux-kernel@...r.kernel.org
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Nadav Amit <namit@...technion.ac.il>, x86@...nel.org,
        Wanpeng Li <wanpengli@...cent.com>, kvm@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Joerg Roedel <joro@...tes.org>,
        Jim Mattson <jmattson@...gle.com>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        David Edmondson <david.edmondson@...cle.com>
Subject: [PATCH] KVM: x86: clflushopt should be treated as a no-op by emulation

The instruction emulator ignores clflush instructions, yet fails to
support clflushopt. Treat both similarly.

Fixes: 13e457e0eebf ("KVM: x86: Emulator does not decode clflush well")
Signed-off-by: David Edmondson <david.edmondson@...cle.com>
---
 arch/x86/kvm/emulate.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 0d917eb70319..56cae1ff9e3f 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4046,6 +4046,12 @@ static int em_clflush(struct x86_emulate_ctxt *ctxt)
 	return X86EMUL_CONTINUE;
 }
 
+static int em_clflushopt(struct x86_emulate_ctxt *ctxt)
+{
+	/* emulating clflushopt regardless of cpuid */
+	return X86EMUL_CONTINUE;
+}
+
 static int em_movsxd(struct x86_emulate_ctxt *ctxt)
 {
 	ctxt->dst.val = (s32) ctxt->src.val;
@@ -4585,7 +4591,7 @@ static const struct opcode group11[] = {
 };
 
 static const struct gprefix pfx_0f_ae_7 = {
-	I(SrcMem | ByteOp, em_clflush), N, N, N,
+	I(SrcMem | ByteOp, em_clflush), I(SrcMem | ByteOp, em_clflushopt), N, N,
 };
 
 static const struct group_dual group15 = { {
-- 
2.28.0