From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f201.google.com (mail-pl1-f201.google.com [209.85.214.201]) (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 837B725A2DB for ; Tue, 11 Feb 2025 18:53:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739299994; cv=none; b=NXQro7lI1d6My9CSZLZEiEpH4U0fkTtoD+OpSzQLGwAKgRnkaLcTvGai4KIJnYRbYKPjBb9kUn5eUs0YWhRv7Pgzd4u05/ekn6h3o4RuquQY/GahyokYogJZncBoLkgNSVIUWlXpRPTYJOsvs+JblowC9Y3YdrN5zoFfpmwzNOk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739299994; c=relaxed/simple; bh=yYcU2JZAoQo0PdjybSDTkRZ6mPUenfDV1ftO6rPg5Uc=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=dwtoATi+eU64Yzwj36sy1KFJ5dz22DX7n4Pu+K/OtbccHAGh3Y6E8lBNJ1eOzPYBUA7+bc7TRFjQf0qfsLEuu5uv2OE2o5EP6MIsIPOoZJqjlOfh0OnTRlIkH483gxSMmGu54EN5JB2osN6ZjKZofxZ/n2RbAvNN9TGLGMSbmMA= 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=wVfmklPW; arc=none smtp.client-ip=209.85.214.201 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="wVfmklPW" Received: by mail-pl1-f201.google.com with SMTP id d9443c01a7336-220bc75098fso620435ad.2 for ; Tue, 11 Feb 2025 10:53:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1739299993; x=1739904793; 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=hSdXzw5i+XGLoyBoJnanrigNUDo0sEg9JmDuJ0DaxPQ=; b=wVfmklPWmdKqL1wwIhnKrVwNMDsl8ft9pm3I3k5WtiVdqR1raSyrxwFcTtogrLTCWl IZXbLBjggkMZ/2owg48P+BHLt5hAS6vcWE6q4s+3mMwOtBue6PzJUGbFCojkbcId9pl/ MrIqm49u17Jh27PIZuO66G3rLKFZH0Hr0wOPBj5jwZ8WSLBkAycysuegAZwX65rFtXVj CPnkpIRc4Nl+k1NvOmIkUaKSEXXSGcOkGyyIxpAou1ahisovocJKRiM252/E+xDUo3oo unrQxnMO4zqR0gTNwmnBxa/kaqjKMGmcpUi+QpyZOu6ZWZmLYWyjYzV8FMMefpEhZICI lZhg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1739299993; x=1739904793; 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=hSdXzw5i+XGLoyBoJnanrigNUDo0sEg9JmDuJ0DaxPQ=; b=P/QcRTW5FZNtYGE2vE9Hvtbs85GUjPcDiIGBxYXi+kYAqvbkk5E91OZ8IulKfn3Rej 6Xc21apxLbmlBT8eE2JcCKpdTsfCMNmA9ek1fF+rcu5/N23IpktBPeouRcp/Z+F37Zjj 95avFtQlju9UnMqhwdHr7tRDIop3+5Fww6zqjwQKywfDdnp7fwasRD0Fn0KE/HklSbeY 49CBViGvFnSm7vMjIc5zdvUcP4jt7mam/cycXh51rvvISF0PE3I4MW07VsNx7VNwaDLa 2EU/tPMbiR0no6SP+vTiVNqv4Mqag7ulxLD3FHSZuSzVq91JNq1bIQrw3XnI8Terpd9l 9Jag== X-Forwarded-Encrypted: i=1; AJvYcCUKRWFAxGYtHItI0gKIvOelTndV/NGTXZ1xyjC5ao5W5ox3MVWW9LhuGFNZg3SX4iUWyTFzMJ2XLjw=@vger.kernel.org X-Gm-Message-State: AOJu0YwteAMuDGxwI4ZEdduGULmekvY2HnHwwMyqPV3Qqgyt2wjsKvbu mY5tu8v3S0gFNK1mcfsnvlZeiT40cshkM24M0LucWGjFAW209VE3z3Y/i5khl7Rq34vXp32WAXw 8WQ== X-Google-Smtp-Source: AGHT+IFX8Gb8h6J+XoaDUIOL0BfhgtQAHFbQcWrM3kh7lUuCjN0+4w5jTeoVicZi2AD+wRaXv1IpPGRPdQY= X-Received: from pgc1.prod.google.com ([2002:a05:6a02:2f81:b0:ad8:6337:811d]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a21:7314:b0:1ed:7540:45d5 with SMTP id adf61e73a8af0-1ee5c74ccf3mr617940637.17.1739299992823; Tue, 11 Feb 2025 10:53:12 -0800 (PST) Date: Tue, 11 Feb 2025 10:53:11 -0800 In-Reply-To: <20241127172654.1024-2-kalyazin@amazon.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20241127172654.1024-1-kalyazin@amazon.com> <20241127172654.1024-2-kalyazin@amazon.com> Message-ID: Subject: Re: [PATCH 1/2] KVM: x86: async_pf: remove support for KVM_ASYNC_PF_SEND_ALWAYS From: Sean Christopherson To: Nikita Kalyazin Cc: pbonzini@redhat.com, corbet@lwn.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, vkuznets@redhat.com, xiaoyao.li@intel.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, roypat@amazon.co.uk, xmarcalx@amazon.com Content-Type: text/plain; charset="us-ascii" On Wed, Nov 27, 2024, Nikita Kalyazin wrote: > 3a7c8fafd1b42adea229fd204132f6a2fb3cd2d9 ("x86/kvm: Restrict > ASYNC_PF to user space") stopped setting KVM_ASYNC_PF_SEND_ALWAYS in > Linux guests. While the flag can still be used by legacy guests, the > mechanism is best effort so KVM is not obliged to use it. What's the actual motivation to remove it from KVM? I agreed KVM isn't required to honor KVM_ASYNC_PF_SEND_ALWAYS from a guest/host ABI perspective, but that doesn't mean that dropping a feature has no impact. E.g. it's entirely possible removing this support could negatively affect a workload running on an old kernel. Looking back at the discussion[*] where Vitaly made this suggestion, I don't see anything that justifies dropping this code. It costs KVM practically nothing to maintain this code. [*] https://lore.kernel.org/all/20241118130403.23184-1-kalyazin@amazon.com