From:   Emanuele Giuseppe Esposito <eesposit@redhat.com>
To:     kvm@vger.kernel.org
Cc:     Jim Mattson <jmattson@google.com>,
        Ben Serebrin <serebrin@google.com>,
        Peter Shier <pshier@google.com>,
        Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Maxim Levitsky <mlevitsk@redhat.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org,
        Emanuele Giuseppe Esposito <eesposit@redhat.com>
Subject: [PATCH 3/3] kvm: x86: Advertise FLUSH_L1D to user space
Date:   Wed,  1 Feb 2023 08:29:05 -0500
Message-Id: <20230201132905.549148-4-eesposit@redhat.com>
In-Reply-To: <20230201132905.549148-1-eesposit@redhat.com>
References: <20230201132905.549148-1-eesposit@redhat.com>
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FLUSH_L1D was already added in 11e34e64e4103, but the feature is not
visible to userspace yet.

The bit definition:
CPUID.(EAX=7,ECX=0):EDX[bit 28]

If the feature is supported by the host, kvm should support it too so
that userspace can choose whether to expose it to the guest or not.
One disadvantage of not exposing it is that the guest will report
a non existing vulnerability in
/sys/devices/system/cpu/vulnerabilities/mmio_stale_data
because the mitigation is present only if the guest supports
(FLUSH_L1D and MD_CLEAR) or FB_CLEAR.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 arch/x86/kvm/cpuid.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 2a9f1e200dbc..9c70cbb663a2 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -649,7 +649,7 @@ void kvm_set_cpu_caps(void)
 		F(SPEC_CTRL_SSBD) | F(ARCH_CAPABILITIES) | F(INTEL_STIBP) |
 		F(MD_CLEAR) | F(AVX512_VP2INTERSECT) | F(FSRM) |
 		F(SERIALIZE) | F(TSXLDTRK) | F(AVX512_FP16) |
-		F(AMX_TILE) | F(AMX_INT8) | F(AMX_BF16)
+		F(AMX_TILE) | F(AMX_INT8) | F(AMX_BF16) | F(FLUSH_L1D)
 	);
 
 	/* TSC_ADJUST and ARCH_CAPABILITIES are emulated in software. */
-- 
2.39.1