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b=49oT5ttofIenxDEArA1ajL2eiYk9WsaiKmCnnTkkZeq5917jRaTOgsqU3F7lbkmFfcH8L6pVeloneSB738HyG24FiQEAro5lgVNmnh0pGOhmus3BL5WtdOLYMN87GJTenjv7ZLZARh05qUkViW44XrlkWOuPrXuzrxG/uLMedCU= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from DM4PR12MB5070.namprd12.prod.outlook.com (2603:10b6:5:389::22) by IA1PR12MB7614.namprd12.prod.outlook.com (2603:10b6:208:429::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8534.44; Wed, 2 Apr 2025 20:41:29 +0000 Received: from DM4PR12MB5070.namprd12.prod.outlook.com ([fe80::20a9:919e:fd6b:5a6e]) by DM4PR12MB5070.namprd12.prod.outlook.com ([fe80::20a9:919e:fd6b:5a6e%5]) with mapi id 15.20.8534.043; Wed, 2 Apr 2025 20:41:28 +0000 Message-ID: <1e34033b-3e3a-bd23-af5a-866e68d5a98a@amd.com> Date: Wed, 2 Apr 2025 15:41:25 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Subject: Re: [PATCH v3 2/6] x86/bugs: Use SBPB in __write_ibpb() if applicable Content-Language: en-US To: Josh Poimboeuf , x86@kernel.org Cc: linux-kernel@vger.kernel.org, amit@kernel.org, kvm@vger.kernel.org, amit.shah@amd.com, bp@alien8.de, tglx@linutronix.de, peterz@infradead.org, pawan.kumar.gupta@linux.intel.com, corbet@lwn.net, mingo@redhat.com, dave.hansen@linux.intel.com, hpa@zytor.com, seanjc@google.com, pbonzini@redhat.com, daniel.sneddon@linux.intel.com, kai.huang@intel.com, sandipan.das@amd.com, boris.ostrovsky@oracle.com, Babu.Moger@amd.com, david.kaplan@amd.com, dwmw@amazon.co.uk, andrew.cooper3@citrix.com References: From: Tom Lendacky In-Reply-To: Content-Type: text/plain; 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If the CPU has SRSO_NO, or if the SRSO mitigation > has been disabled, branch type flushing isn't needed, in which case the > lighter-weight SBPB can be used. Maybe add something here that indicates the x86_pred_cmd variable tracks this optimization so switch to using that variable vs the hardcoded IBPB? Thanks, Tom > > Signed-off-by: Josh Poimboeuf > --- > arch/x86/entry/entry.S | 2 +- > arch/x86/kernel/cpu/bugs.c | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/entry/entry.S b/arch/x86/entry/entry.S > index 3a53319988b9..a5b421ec19c0 100644 > --- a/arch/x86/entry/entry.S > +++ b/arch/x86/entry/entry.S > @@ -21,7 +21,7 @@ > SYM_FUNC_START(__write_ibpb) > ANNOTATE_NOENDBR > movl $MSR_IA32_PRED_CMD, %ecx > - movl $PRED_CMD_IBPB, %eax > + movl _ASM_RIP(x86_pred_cmd), %eax > xorl %edx, %edx > wrmsr > > diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c > index 310cb3f7139c..c8b8dc829046 100644 > --- a/arch/x86/kernel/cpu/bugs.c > +++ b/arch/x86/kernel/cpu/bugs.c > @@ -58,7 +58,7 @@ EXPORT_SYMBOL_GPL(x86_spec_ctrl_base); > DEFINE_PER_CPU(u64, x86_spec_ctrl_current); > EXPORT_PER_CPU_SYMBOL_GPL(x86_spec_ctrl_current); > > -u64 x86_pred_cmd __ro_after_init = PRED_CMD_IBPB; > +u32 x86_pred_cmd __ro_after_init = PRED_CMD_IBPB; > EXPORT_SYMBOL_GPL(x86_pred_cmd); > > static u64 __ro_after_init x86_arch_cap_msr;