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 84DF125A323 for ; Tue, 11 Feb 2025 18:53:13 +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=1739299995; cv=none; b=ph+qX2hPiIOmwifluFhnzkhh2iXAOMEvRrWwSqFMvwH7UG1NI15Xck6oNGfpUjar7bw52MmO5DHhfK8F2+CoXaquDsdVw05fAyHTqB/PgcXoUpW7Y2eu9DBdC83L3JKM8uVKh7iXuJ7OP/cK/fAtj8Pj2Xi7mwdsN/Dh8Yx3+l4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739299995; c=relaxed/simple; bh=yYcU2JZAoQo0PdjybSDTkRZ6mPUenfDV1ftO6rPg5Uc=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=Ea9TPfgKBtrUHrnVnZJlJjX3MhzwzDayKhiq4JvA2Tao/mHOZtTu+TVf7zRzY7167imL5R6pvz9oPiJ2JW2/yoa7IJ3fSbc5V03FqaJNnwvrTSjjVRyojk2b5ZgpegEZTxjpvn723p/ybCy2tVRo3MWwGUOgFvQ1RJ2D4/eQ/I4= 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=209.85.214.202 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="wVfmklPW" Received: by mail-pl1-f202.google.com with SMTP id d9443c01a7336-21f61a983ddso146146205ad.1 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=Ss2iz4lPS8TSi0J8EFIfzYvPXjlJ5GLK5u0U6dNvsyiUYC3vkcgDTq9+sokijK59rQ 7KNMeZuPBl3hUZX6ykQc/rto1zlI1q6iyRosrtc1m+Y16BVTeUivlGozZ2Oa3yuHzEby ehQ4GZZ88EYq/RwWEcgKer3x1Dcc00gx0AbNnqAsUV9osQxcY1b0yWsUgxejKYUTFz7c FHt2bMtidZqZ45nobEeSXAhWV6PcCIcT5OLuO+t/SGrP+/GOa6u6cxnlJYzVKOaST5s2 42BHmTOa9xI/qcuk6f0HJKWwQ51OK64SpujmJfneOCMj5l/IV+TZ/vGRKqyAuJDvKjsO n3tw== X-Forwarded-Encrypted: i=1; AJvYcCU9JXbkPVOZQfVEdYrkQ3ydD4GCibkGXmWEk7cj5bgAEZ+VAy7kmmfowZ3K0hmDpYmveJ4GJ7n8K9O7ro8=@vger.kernel.org X-Gm-Message-State: AOJu0YwPx9W4XWEJYNH/CIDXLSSeBvNtRa/mtKyratcBeDPlTVfTbFY6 DGrNK+NWNWaXyuqM516Ykh9OfZ/9ohSJCCzkKx60XzN4BrPG/FjY8uW9h7JUkCKHbjmM7aAs1Ye SZA== 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-kernel@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