linux-kernel - [PATCH 1/5] x86/cpufeatures: Introduce X86_FEATURE_NO

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Message-ID: <20220916045832.461395-2-jmattson@google.com>
Date:   Thu, 15 Sep 2022 21:58:28 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Avi Kivity <avi@...hat.com>, Babu Moger <babu.moger@....com>,
        Borislav Petkov <bp@...en8.de>,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Joerg Roedel <joerg.roedel@....com>,
        Josh Poimboeuf <jpoimboe@...nel.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Wyes Karny <wyes.karny@....com>, x86@...nel.org
Cc:     Jim Mattson <jmattson@...gle.com>
Subject: [PATCH 1/5] x86/cpufeatures: Introduce X86_FEATURE_NO_LMSLE

When AMD introduced "Long Mode Segment Limit Enable" (a.k.a. "VMware
mode"), the feature was not enumerated by a CPUID bit. Now that VMware
has abandoned binary translation, AMD has deprecated EFER.LMSLE.

The absence of the feature *is* now enumerated by a CPUID bit (a la
Intel's X86_FEATURE_ZERO_FCS_DCS and X86_FEATURE_FDP_EXCPTN_ONLY).

This defeature bit is already present in feature word 13, but it was
previously anonymous. Name it X86_FEATURE_NO_LMSLE, so that KVM can
reference it when deciding whether or not EFER.LMSLE should be a
reserved bit in a KVM guest.

Since this bit indicates the absence of a feature, don't enumerate it
in /proc/cpuinfo.

Signed-off-by: Jim Mattson <jmattson@...gle.com>
---
 arch/x86/include/asm/cpufeatures.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index ef4775c6db01..0f5a3285d8d8 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -319,6 +319,7 @@
 #define X86_FEATURE_AMD_IBRS		(13*32+14) /* "" Indirect Branch Restricted Speculation */
 #define X86_FEATURE_AMD_STIBP		(13*32+15) /* "" Single Thread Indirect Branch Predictors */
 #define X86_FEATURE_AMD_STIBP_ALWAYS_ON	(13*32+17) /* "" Single Thread Indirect Branch Predictors always-on preferred */
+#define X86_FEATURE_NO_LMSLE		(13*32+20) /* "" EFER_LMSLE is unsupported */
 #define X86_FEATURE_AMD_PPIN		(13*32+23) /* Protected Processor Inventory Number */
 #define X86_FEATURE_AMD_SSBD		(13*32+24) /* "" Speculative Store Bypass Disable */
 #define X86_FEATURE_VIRT_SSBD		(13*32+25) /* Virtualized Speculative Store Bypass Disable */
-- 
2.37.3.968.ga6b4b080e4-goog