From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f41.google.com (mail-wr1-f41.google.com [209.85.221.41]) (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 6E2243CFF6A for ; Wed, 29 Apr 2026 10:36:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.41 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777459017; cv=none; b=almhusXhZO3uJjsigMZVzAWwXcpveMlT2vmv2w+bJCL624Ezj/qmaO118G3LkGV6Vyk+K6Lki5pBDaPjJZpHHqnDbFZKCU1oKqrcsOi7hZA3vHK58PeycfOGbGBVPcggehDWN3Qt8KQkzTTeRJ2zR3GxzsUImD7W5kDPJcFI9Fw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777459017; c=relaxed/simple; bh=/oOkSzD6qmVsvpsVH9AtHt7dJBZc2mXnlIq7kZZektI=; h=From:Message-ID:Date:MIME-Version:Subject:To:References: In-Reply-To:Content-Type; b=P1j6XkspXmkrs6bbrZnZCR7QaUaaUay2ivaNoCdlpxat9eEuwPFPzf0t4Lv7y888L8bnBfX65INY5JkvlEDmr+5qMPVOaKJRmGqfUosJwEe/uvrER0C44dbCrQPGGq3wFruFi0nKPi8+qAu1xmRVgf8F2HgkeEH304oyWqjyhMY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=T9ZAIYPq; arc=none smtp.client-ip=209.85.221.41 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="T9ZAIYPq" Received: by mail-wr1-f41.google.com with SMTP id ffacd0b85a97d-43fe8bda8e9so6931236f8f.1 for ; Wed, 29 Apr 2026 03:36:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1777459015; x=1778063815; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:content-language:references :to:subject:user-agent:mime-version:date:message-id:from:from:to:cc :subject:date:message-id:reply-to; bh=a88lVFGd0bTcNDpi0vvKuLvilGml+v2O2rcvl8VmwI0=; b=T9ZAIYPqkBrI8o4vQs7lkXaGcAZZ/KN6BWBrATmeNr6SSDOC7owEXslRXlb8PL0O30 KJoQrtC+/DjmFwWmRVIwNwgOI+N8RtCYhcmSsSA5b+YJyGC8aUt+svYSB93VUyj/CqBe vNinq6lDEU8XDXnqBJGccuAD4m4oTynYNDWVDGtZ3kRFBRz8I7VoXX1zZy6na+9P7vzV bTKg5Wlj25+mJyYhGA0bARJ2ecS6vICa6incCd2bNw8hZ0LvoZYPJJW3xp3FFmIQ1qHY O+0pQklqKVKW8a/rW/szcnKAS2CbMt4mIXSBPofoHuX17igNW/9xmI8hp2HeI1UrhHDI FI0A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1777459015; x=1778063815; h=content-transfer-encoding:in-reply-to:content-language:references :to:subject:user-agent:mime-version:date:message-id:from:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=a88lVFGd0bTcNDpi0vvKuLvilGml+v2O2rcvl8VmwI0=; b=LcchfygeLy771bGaHfJTbuEtC9PfS8S0YghBPR+h8SobOtYcvRblB/7FwBT7Wrw/7/ z4lCKqSlf64POGsgFlQXXShxX9P1Ryl8D8NFxLgANbRVXl1TTG0YU5Sle9eCvHATOJ85 ygoOhDcvyIfBWT7XUGlX+KSRMXUER5f4iSSHZB1crf8k7O5YnUOgzzxrgsPNCri9qBpG f4YtpljmKAM5A+jUwfw6ElJ43JyZU9u54xWiFp1FgvMyxlFc0hYawLikTpSrm/dhU4Yr dlR9mA5H2kR78KDWg+x7PDelcroy1e5S4gEthc0z6hU9jyNkgqhJOAwJZbKYFe5m9Yen bzLQ== X-Forwarded-Encrypted: i=1; AFNElJ81pj9lvMxqby5GZ50Fvqhlnos6vnHuXo2HkZqKYt6uYMzDA58Vt6yffAHsqrfIyBvpyaevrSdAFTA=@vger.kernel.org X-Gm-Message-State: AOJu0Yy34nNWVTZEb27ytlBALyp0bmDoXFP8qZOdMixyGIxLrAMHZtoZ yIrD5ql2H7/C1V/4kaJcISHc6mGdEdYWADahs5WgUTmpD7BS1yQjvinG X-Gm-Gg: AeBDiev+uWDIJXwj7saDZygqxn95Tye7JAIx7HKzzlsARntx9lac54fOrkMcGdCT0lu vOYeKkUYolS/Z6dubwSzRzmlGkOSJlKWMUN6CXsv2E7d6SSpsNa+oQ0GJpLwbFPW0ArfHa25aa9 SJlKh3iloSkjqR85Ye9LG2tkV9/Nr4g4Bf2IlH9P1EnXmHKNc5lzwVV98+phEC4UdcYYeoJAt3q Hq4+4uN/f8Ah0PN3uXT/+098u3H/8AeXYLHx1Ff56xU6eYB9f2hDVKHerF+r8dcS7HR1u/k+K01 weTIgzICNldpJ2M67O3b6/pKFL0htcLicrrbCCWN8anDzy9Xl6k36wqV2KuOrfKqytOaDofadHh NtskbXDwXibEZVyrwdBH1mwOXu2AXjU3lgVtpNzBGCHVmOjH+aaBrNJnf1GS32sPsbuF7Ix/Z4m SSmlBJMj8VcJ3CPCalQyNnXeNjPksXKKx690Xa2ek= X-Received: by 2002:a05:6000:1884:b0:43e:b0dd:396b with SMTP id ffacd0b85a97d-4464a4470aemr12037851f8f.25.1777459014631; Wed, 29 Apr 2026 03:36:54 -0700 (PDT) Received: from [10.4.211.108] ([15.248.2.52]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-447b7217c2asm4556829f8f.19.2026.04.29.03.36.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 29 Apr 2026 03:36:54 -0700 (PDT) From: Paul Durrant X-Google-Original-From: Paul Durrant Message-ID: Date: Wed, 29 Apr 2026 12:36:52 +0200 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] KVM: x86/xen: Add KVM_XEN_VCPU_ATTR_TYPE_WRITE_HYPERCALL_PAGE To: David Woodhouse , Paolo Bonzini , Jonathan Corbet , Shuah Khan , Sean Christopherson , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org References: Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 28/04/2026 21:12, David Woodhouse wrote: > From: David Woodhouse > > Commit 3617c0ee7decb ("KVM: x86/xen: Only write Xen hypercall page for > guest writes to MSR") blocked host-initiated writes from triggering the > Xen hypercall page setup, to fix an SRCU usage violation when the > hypercall MSR index collides with a real MSR written during vCPU reset. > > However, some VMMs legitimately need to trigger hypercall page setup > from host context. For example, a VMM may intercept the guest's MSR > write to track an epoch (for kexec/crash recovery), and then replay the > write as a host-initiated KVM_SET_MSRS to populate the hypercall page. > The host_initiated check breaks this use case. > > Add KVM_XEN_VCPU_ATTR_TYPE_WRITE_HYPERCALL_PAGE as a new vcpu attribute > that explicitly invokes kvm_xen_write_hypercall_page() under proper > locking. This gives userspace a safe interface to trigger hypercall page > setup without going through the MSR write path, preserving the > host_initiated defence in depth while restoring the lost functionality. > > Fixes: 3617c0ee7dec ("KVM: x86/xen: Only write Xen hypercall page for guest writes to MSR") > Signed-off-by: David Woodhouse > --- > Documentation/virt/kvm/api.rst | 11 +++ > arch/x86/include/uapi/asm/kvm.h | 3 + > arch/x86/kvm/x86.c | 3 +- > arch/x86/kvm/xen.c | 7 ++ > .../selftests/kvm/x86/xen_vmcall_test.c | 96 +++++++++++++++++++ > 5 files changed, 119 insertions(+), 1 deletion(-) > Reviewed-by: Paul Durrant