From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f202.google.com (mail-pl1-f202.google.com [209.85.214.202]) (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 55C5B1E766D for ; Tue, 5 Nov 2024 19:18:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730834299; cv=none; b=JXC3rfHFzsm8VLS7j2my9w4/1MWPcBaxoyS2mrAoaL+PLP3o/xnRm7A6GeGwqLcGqK4Qa6b2zBpcjMHJqcPl8JhVdnrU1R7/Fwl7hX3m17VQVH9MW5VhkXFEifj+7LMSnB+jJZ1StwgmIBPD5/RUWo/k1ocrQyu6OuXCRqoAqk8= 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=209.85.214.202 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-pl1-f202.google.com with SMTP id d9443c01a7336-20c2cffd698so62655355ad.2 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=tooBRjGv5EcKzlBBuVp08e9CfYLk/Do7dm/HxbOScycSb7HO04Un2llXj+i4U5ixNE 6JDPNeenkW8UchVnUgxb8Q8SuAm4W3k3TQVDDoejWI2s23kSlPq1jx/HKwpIy8500cyc HujXrqjDRhpIi/Vfv/gBbicokRhWKJH+gSPTBci9qf6gnAkJNY5tLMJifBnxnppa7rsK 9nfcB/cBVh32cppmC6estn7GlV8doQXtxFMRZv1wvN4un52uwlSNrPynIa0J6FFfXLLK aLBfpl5WwykE/SPAjI5P8erDb2E5VhjLJeqinEM+W8etD4JVi0/KvVEGQussr9/O2XCO 0Z6w== X-Forwarded-Encrypted: i=1; AJvYcCUr5eICb4MFT0m993+IavkiJ7VO+2KpXiNpmiQjT39XRwcGNsmSK7Pr7s1kDQmV1UNgwNWpx80gXwZ91Rw=@vger.kernel.org X-Gm-Message-State: AOJu0YzXs7nGzPuM9Yk1sASAYvgO9uZ+pEhOfLReV9+Uefa+gBaM4Ouo WTyXYKTcB3iZPF4nAqXCD0CSR2YWpvwZEogrpFfgDTdPeprh+XXHEJftGO7r+VPsC0aAW7AjxZX CyQ== 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: linux-kernel@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.