From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f73.google.com (mail-pj1-f73.google.com [209.85.216.73]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 56EE61E7C27 for ; Tue, 5 Nov 2024 19:18:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.73 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730834299; cv=none; b=K/hv9GbPfM1+x2IebRrHqn2Xb2BIlbpkLlbt7+dn1BNDidFck/aYVkhwZb43AnAl/qSaIZflbjYrkTNrM7siVh9lli41N3vTIAn2XXFeWPgcdj32lmU7QwvLMw36iapa58Lqsu8vgdOGQde4YrhmU8WJ7SuDgc1nKeeoLuj4Y98= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730834299; c=relaxed/simple; bh=KcLNmdINbboEOcPBnOOngbnVFtKqG1jrQP932oLB02k=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=fNS/iu53j88tZxEFagTIb7UJg4R+YVFb6T+6MgrUg9BAc2HcYhFcVwf7qNcPBX4htOrDLHc1BSjK8Rqu5nV/ZVG6FyCR9XBLYDBVa79H70aBGSqAqC+QfvjkwvXMpd+qRqatCBN70njka/zslEvrTFqvoqA9FFkaRqbqDpDDdRs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=jrygHNjt; arc=none smtp.client-ip=209.85.216.73 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="jrygHNjt" Received: by mail-pj1-f73.google.com with SMTP id 98e67ed59e1d1-2e5a60d8af1so5587259a91.1 for ; Tue, 05 Nov 2024 11:18:18 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1730834298; x=1731439098; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=9f4OfL/WzG7jWvwRWk9HMZifJUGYJMKeOzFPitEAUFc=; b=jrygHNjtZKGCqBn6FUXaLqHFlbU5FDIR5klRoMU/5AETQ6YEZdEIVGUegGV2GtckbS JJQ5oTsq8onF/9Oew4FNOOkXtuEpa+CRlGNBsisxko+bCrM+Rz2H3sT8N5vAMzPzG1qY h4GiRYQkWubfA1u1aBCWDIuMtlZd+I/SpIEJpG0yOnrlC5sagu5+p/+sP2oAg3udSy7X klwciuAS/vid1kwFBW9vSAsF1IjFVYOD+IOLsEgSaFc3jfgmXsvQINFEmFzelNilvaSr xrq8xhEI7SpBxl8Py0vJ1Hc+A2QOaERT0/DGf9r0F4dw42dD1VmG9hiKIodmI/J5CpfR kLCQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1730834298; x=1731439098; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=9f4OfL/WzG7jWvwRWk9HMZifJUGYJMKeOzFPitEAUFc=; b=p2dEkx+2fZlfxj5CIcakkIfMdTkiOVvoja9oD2k2nT4NYNwcKWtvpoaAWkS8Tvy93X cSIVWjwidcfvDMvC3++mVDLJzwOGtouZPqza4ikfEPpjiwqzfEe6Axq9dtLOQkWz2WFX ymDg3CsztAU38GyUXURxdkv+q5MwfJJeSytfL+96LOXnp3RsWZ6xbZBpC3ZiiDDUvk22 qvzC9jITA9qB4JBBGikSQK2tJzI+DFPIy8rn2w0l6BxPvbjBhk2Pg9/yiSM0KG32DnbA k3YGsA6sNsdz3dZLSmT5G/fMoPplELVpcHG9aNP/8sL3TFoDJ/lgO+8LBpPd2MqTgKQh eKIg== X-Forwarded-Encrypted: i=1; AJvYcCVGvaXOTAK3HxMl10KlIpfwMT+odfo7a1Sp5Tm/ERTLsYGnQINOFUrWbub3KfLK0zziFBM=@vger.kernel.org X-Gm-Message-State: AOJu0YxWn6grfEvqO8NckrqdUpuUjOCuSwsOse27OFJuS1v7ydiWHmO0 VG+z1igz0lYdhvUS49/mQzp2cijcx2QsYLrSLH8md04txR4rI11cW+xyfm2z1Z1IY+fheKR3+0u XJA== X-Google-Smtp-Source: AGHT+IHMYuAZnXAc/S1cVTWe83OJa2YM6NdR95YJGJDDiTdYVajYkwQdrKNrGa/D+hjmRYf6j640qi+2ZIM= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:9d:3983:ac13:c240]) (user=seanjc job=sendgmr) by 2002:a17:90a:a40e:b0:2e2:d3d2:347 with SMTP id 98e67ed59e1d1-2e94c51d7c1mr31265a91.6.1730834297611; Tue, 05 Nov 2024 11:18:17 -0800 (PST) Date: Tue, 5 Nov 2024 11:18:16 -0800 In-Reply-To: <20241105185622.GEZypqVul2vRh6yDys@fat_crate.local> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20241104101543.31885-1-bp@kernel.org> <20241105123416.GBZyoQyAoUmZi9eMkk@fat_crate.local> <20241105185622.GEZypqVul2vRh6yDys@fat_crate.local> Message-ID: Subject: Re: [PATCH] x86/bugs: Adjust SRSO mitigation to new features From: Sean Christopherson To: Borislav Petkov Cc: Borislav Petkov , X86 ML , Josh Poimboeuf , Pawan Gupta , kvm@vger.kernel.org, LKML Content-Type: text/plain; charset="us-ascii" On Tue, Nov 05, 2024, Borislav Petkov wrote: > On Tue, Nov 05, 2024 at 10:10:20AM -0800, Sean Christopherson wrote: > > All of the actual maintainers. > > Which maintainers do you mean? tip ones? If so, they're all shorted to > x86@kernel.org. > > > AFAIK, Paolo doesn't subscribe to kvm@. > > Oh boy, srsly?! I thought I'd reach the proper crowd with > kvm@vger.kernel.org... It gets there, usually (as evidenced by my response). But even for me, there's a non-zero chance I'll miss something that's only Cc'd to kvm@, largely because kvm@ is used by all things virt, i.e. it's a bit noisy: $ git grep kvm@ MAINTAINERS | wc -l 29 > > What does the bit actually do? I can't find any useful documentation, and the > > changelog is equally useless. > > "Processors which set SRSO_MSR_FIX=1 support an MSR bit which mitigates SRSO > across guest/host boundaries. Software may enable this by setting bit > 4 (BpSpecReduce) of MSR C001_102E. This bit can be set once during boot and > should be set identically across all processors in the system." > > From: https://www.amd.com/content/dam/amd/en/documents/corporate/cr/speculative-return-stack-overflow-whitepaper.pdf > > I think that's the only public info we have on that bit. Heh, I found that. Not very helpful. If you can't document the specifics, can you at least describe the performance implications? It's practically impossible to give meaningful feedback without having any idea what the magic bit does.