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b=pbXr0ycr5aq7nh7lowwXGZmOLulejJ7H/ReuNym215OyCPO2VYGZBWLBymriyRVEmT4D+eo2y6y76mVpHnLR47ZXwA9H02kxoA8ERtrlgLq9DkufocXr6EAX/hwpAYuj1S5g1DnGW4dWC1F4ywO+x0YO+a5cVP5yG8sM0ixvdm4= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from DS7PR12MB6214.namprd12.prod.outlook.com (2603:10b6:8:96::13) by PH8PR12MB7254.namprd12.prod.outlook.com (2603:10b6:510:225::18) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.7875.29; Thu, 22 Aug 2024 09:43:19 +0000 Received: from DS7PR12MB6214.namprd12.prod.outlook.com ([fe80::17e6:16c7:6bc1:26fb]) by DS7PR12MB6214.namprd12.prod.outlook.com ([fe80::17e6:16c7:6bc1:26fb%5]) with mapi id 15.20.7875.019; Thu, 22 Aug 2024 09:43:18 +0000 Message-ID: <11485f4f-1d26-4320-9d2a-2032a8e19653@amd.com> Date: Thu, 22 Aug 2024 15:13:08 +0530 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v1 1/4] x86/cpufeatures: Add CPUID feature bit for the Bus Lock Threshold To: Sean Christopherson Cc: kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, pbonzini@redhat.com, shuah@kernel.org, nikunj@amd.com, thomas.lendacky@amd.com, vkuznets@redhat.com, bp@alien8.de, babu.moger@amd.com, Manali Shukla References: <20240709175145.9986-1-manali.shukla@amd.com> <20240709175145.9986-2-manali.shukla@amd.com> Content-Language: en-US From: Manali Shukla In-Reply-To: Content-Type: text/plain; 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On 8/17/2024 1:07 AM, Sean Christopherson wrote: > On Tue, Jul 09, 2024, Manali Shukla wrote: >> Malicious guests can cause bus locks to degrade the performance of > > I would say "misbehaving", I bet the overwhelming majority of bus locks in practice > are due to legacy/crusty software, not malicious software. > Ack. >> a system. Non-WB(write-back) and misaligned locked >> RMW(read-modify-write) instructions are referred to as "bus locks" and >> require system wide synchronization among all processors to guarantee >> atomicity. The bus locks may incur significant performance penalties >> for all processors in the system. >> >> The Bus Lock Threshold feature proves beneficial for hypervisors >> seeking to restrict guests' ability to initiate numerous bus locks, >> thereby preventing system slowdowns that affect all tenants. > > None of this actually says what the feature does. > Sure I will rewrite the commit message. >> Presence of the Bus Lock threshold feature is indicated via CPUID >> function 0x8000000A_EDX[29] >> >> Signed-off-by: Manali Shukla >> --- >> 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 3c7434329661..10f397873790 100644 >> --- a/arch/x86/include/asm/cpufeatures.h >> +++ b/arch/x86/include/asm/cpufeatures.h >> @@ -381,6 +381,7 @@ >> #define X86_FEATURE_V_SPEC_CTRL (15*32+20) /* Virtual SPEC_CTRL */ >> #define X86_FEATURE_VNMI (15*32+25) /* Virtual NMI */ >> #define X86_FEATURE_SVME_ADDR_CHK (15*32+28) /* "" SVME addr check */ >> +#define X86_FEATURE_BUS_LOCK_THRESHOLD (15*32+29) /* "" Bus lock threshold */ > > I would strongly prefer to enumerate this in /proc/cpuinfo, having to manually > query CPUID to see if a CPU supports a feature I want to test is beyond annoying. I will do the modifications accordingly. > >> /* Intel-defined CPU features, CPUID level 0x00000007:0 (ECX), word 16 */ >> #define X86_FEATURE_AVX512VBMI (16*32+ 1) /* AVX512 Vector Bit Manipulation instructions*/ >> >> base-commit: 704ec48fc2fbd4e41ec982662ad5bf1eee33eeb2 >> -- >> 2.34.1 >> - Manali