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([2001:b07:6468:f312:63a7:c72e:ea0e:6045]) by smtp.googlemail.com with ESMTPSA id h3-20020a5d4303000000b0033629538fa2sm4664964wrq.18.2023.12.13.04.52.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 13 Dec 2023 04:52:09 -0800 (PST) Message-ID: Date: Wed, 13 Dec 2023 13:52:07 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 05/50] x86/speculation: Do not enable Automatic IBRS if SEV SNP is enabled To: Michael Roth , kvm@vger.kernel.org Cc: linux-coco@lists.linux.dev, linux-mm@kvack.org, linux-crypto@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, jroedel@suse.de, thomas.lendacky@amd.com, hpa@zytor.com, ardb@kernel.org, seanjc@google.com, vkuznets@redhat.com, jmattson@google.com, luto@kernel.org, dave.hansen@linux.intel.com, slp@redhat.com, pgonda@google.com, peterz@infradead.org, srinivas.pandruvada@linux.intel.com, rientjes@google.com, dovmurik@linux.ibm.com, tobin@ibm.com, bp@alien8.de, vbabka@suse.cz, kirill@shutemov.name, ak@linux.intel.com, tony.luck@intel.com, marcorr@google.com, sathyanarayanan.kuppuswamy@linux.intel.com, alpergun@google.com, jarkko@kernel.org, ashish.kalra@amd.com, nikunj.dadhania@amd.com, pankaj.gupta@amd.com, liam.merwick@oracle.com, zhi.a.wang@intel.com, Kim Phillips References: <20231016132819.1002933-1-michael.roth@amd.com> <20231016132819.1002933-6-michael.roth@amd.com> From: Paolo Bonzini Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 1F1FE1C001E X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: gauh8xw1t1i7rdmkrxjd9fdpixr8xokw X-HE-Tag: 1702471933-7230 X-HE-Meta: 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 U1dlKOcM nESd+Zlq7Il6ygsgAZEN7N+itniXk8/HqAbUGCaUGad9Ose8D9sWOsAkjCFmZISSWhFY0qBNspEm5u+KTOn4T6CQ+jOZMTu7XKoQLxyPxQ+cx6X0Gr1w8RVcFu3fOozr9XGeIi5kx2D4atMDZUbqlX7RAfAj11HYydBnA57PlqzSjtjO2E+hiw0L0o4dwefmW7xT8xJ7n6F9OHDxGtvtMKQfozbu0wCD7hFpHQAcXoNw39RL82UinIPYBPZnupeejswOMbTajpD+wfS/8nruczDDVYKvjRPzOiOPvXLU8b2ok/Kr24idLoOKCxMynvjVtWxKCc/N4d6j9HzaiFKS8NHyPDpHiCcTk1fA9362trPkQ2BOhGaUYrjITZalkliuJD9JUGrYwOIylI3VNWgx43lb388hLNmmogTfA X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/16/23 15:27, Michael Roth wrote: > From: Kim Phillips > > Without SEV-SNP, Automatic IBRS protects only the kernel. But when > SEV-SNP is enabled, the Automatic IBRS protection umbrella widens to all > host-side code, including userspace. This protection comes at a cost: > reduced userspace indirect branch performance. > > To avoid this performance loss, don't use Automatic IBRS on SEV-SNP > hosts. Fall back to retpolines instead. > > Signed-off-by: Kim Phillips > [mdr: squash in changes from review discussion] > Signed-off-by: Michael Roth Queued, thanks. Paolo > --- > arch/x86/kernel/cpu/common.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c > index 382d4e6b848d..11fae89b799e 100644 > --- a/arch/x86/kernel/cpu/common.c > +++ b/arch/x86/kernel/cpu/common.c > @@ -1357,8 +1357,13 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c) > /* > * AMD's AutoIBRS is equivalent to Intel's eIBRS - use the Intel feature > * flag and protect from vendor-specific bugs via the whitelist. > + * > + * Don't use AutoIBRS when SNP is enabled because it degrades host > + * userspace indirect branch performance. > */ > - if ((ia32_cap & ARCH_CAP_IBRS_ALL) || cpu_has(c, X86_FEATURE_AUTOIBRS)) { > + if ((ia32_cap & ARCH_CAP_IBRS_ALL) || > + (cpu_has(c, X86_FEATURE_AUTOIBRS) && > + !cpu_feature_enabled(X86_FEATURE_SEV_SNP))) { > setup_force_cpu_cap(X86_FEATURE_IBRS_ENHANCED); > if (!cpu_matches(cpu_vuln_whitelist, NO_EIBRS_PBRSB) && > !(ia32_cap & ARCH_CAP_PBRSB_NO))