From nobody Wed Apr 1 23:47:01 2026 Delivered-To: importer@patchew.org Received-SPF: pass (zohomail.com: domain of lists.xenproject.org designates 192.237.175.120 as permitted sender) client-ip=192.237.175.120; envelope-from=xen-devel-bounces@lists.xenproject.org; helo=lists.xenproject.org; Authentication-Results: mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of lists.xenproject.org designates 192.237.175.120 as permitted sender) smtp.mailfrom=xen-devel-bounces@lists.xenproject.org; dmarc=pass(p=reject dis=none) header.from=citrix.com ARC-Seal: i=1; a=rsa-sha256; t=1774946492; cv=none; d=zohomail.com; s=zohoarc; b=KG2zK/0RHdVZaEdRmtS6Y0rBvHCrqoL8rkHqq/jsZzLkqpFhOkyr7AZp5Ku29+nklbAr0yw6x1OE4PaJOuAg1tdOPIENFoY9IYBUT9kTY1KMiVXjmwj7z/iz5Nofy0bJdAmbazT86p41v7wR1WwRRkto2fh1wKb1H5zBQXn4Q3I= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1774946492; h=Content-Type:Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:List-Subscribe:List-Post:List-Id:List-Help:List-Unsubscribe:MIME-Version:Message-ID:Sender:Subject:Subject:To:To:Message-Id:Reply-To; bh=TS8VSazZTzGwbY386Zmn1pdmyaz5X0QAPZsATvifGeY=; b=DmI0TlBnD82yqk56hGq9wbNOT64ZsCUFlRjhghOPBoYUwftF8AgnNa2XbxXzqELvCwwbMz3V9DHee4ymQVIyPim/MpJqI65nGukmMpjoZEKSVWiupYeJDx2K46DSaqEFV0uH622KNOGoOkIsRXXQSHdsGb377HOEJF3jY5T9nYQ= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of lists.xenproject.org designates 192.237.175.120 as permitted sender) smtp.mailfrom=xen-devel-bounces@lists.xenproject.org; dmarc=pass header.from= (p=reject dis=none) Return-Path: Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) by mx.zohomail.com with SMTPS id 1774946492863831.6516122763455; Tue, 31 Mar 2026 01:41:32 -0700 (PDT) Received: from list by lists.xenproject.org with outflank-mailman.1268746.1557956 (Exim 4.92) (envelope-from ) id 1w7Uem-0005U7-Rb; Tue, 31 Mar 2026 08:41:04 +0000 Received: by outflank-mailman (output) from mailman id 1268746.1557956; Tue, 31 Mar 2026 08:41:04 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1w7Uem-0005U0-P4; Tue, 31 Mar 2026 08:41:04 +0000 Received: by outflank-mailman (input) for mailman id 1268746; Tue, 31 Mar 2026 08:41:04 +0000 Received: from mx.expurgate.net ([195.190.135.10]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1w7Uem-0005Tu-0E for xen-devel@lists.xenproject.org; Tue, 31 Mar 2026 08:41:04 +0000 Received: from mx.expurgate.net (helo=localhost) by mx.expurgate.net with esmtp id 1w7Uel-00Fjih-1h for xen-devel@lists.xenproject.org; Tue, 31 Mar 2026 10:41:03 +0200 Received: from [10.42.69.12] (helo=localhost) by localhost with ESMTP (eXpurgate MTA 0.9.1) (envelope-from ) id 69cb8890-e002-0a2a0a5209dd-0a2a450c9a10-24 for ; Tue, 31 Mar 2026 10:41:02 +0200 Received: from [209.85.128.43] (helo=mail-wm1-f43.google.com) by tlsNG-d25034.mxtls.expurgate.net with ESMTPS (eXpurgate 4.55.2) (envelope-from ) id 69cb889e-f93d-0a2a450c0019-d155802bec64-3 for ; Tue, 31 Mar 2026 10:41:02 +0200 Received: by mail-wm1-f43.google.com with SMTP id 5b1f17b1804b1-486507134e4so62287075e9.0 for ; Tue, 31 Mar 2026 01:41:02 -0700 (PDT) Received: from andrew-laptop.home ([2a01:cb15:80df:da00:ec5b:e128:36bf:56b1]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4887e93cf2dsm17613825e9.11.2026.03.31.01.41.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Mar 2026 01:41:00 -0700 (PDT) X-Outflank-Mailman: Message body and most headers restored to incoming version X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" Authentication-Results: eu.smtp.expurgate.cloud; dkim=pass header.s=google header.d=citrix.com header.i="@citrix.com" header.h="Content-Transfer-Encoding:MIME-Version:Message-Id:Date:Subject:Cc:To:From" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.com; s=google; t=1774946461; x=1775551261; darn=lists.xenproject.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=TS8VSazZTzGwbY386Zmn1pdmyaz5X0QAPZsATvifGeY=; b=l91yvC5g5T2op+ID4FklrOqhxiWKoYMZESyuJZLttzoeHMpdS2kcE5Uu4xuJ3HM9g8 6KRgUQ5Lt79x3DouYKSVxLQeJcggATOyRmoW83cNV9kx78C44A4TwznXNZQlblGNEvYT 0mURhq5tfYOTvXqm1G6HWY3tovbCyzc1MP1bA= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1774946461; x=1775551261; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=TS8VSazZTzGwbY386Zmn1pdmyaz5X0QAPZsATvifGeY=; b=YKEaiBgMPldfQVnlsYs3ublizbCwHAINoVa0uhdFKNzaMW9WWRSg2KdIg0dEiHi7Cz sO5hjeqH1CfpxBum1O8auS2zSpevAJlk9bRHZdX9ltA20PR4xdsXdcIyvRWCMfZlI6oa q/foZBk/9yajJkPrUgDNPrecLUoB8OyzKsncpSKKGbmeXRKKy7pYJLoRULKiyQFuHbeW 0EAqaoYsoNFROHDWCZ0WfYDJcdAcRSkFAXPYC/BAKPqcg0HoDwCXkaesTM7XBMWVrHmV IolIfe4QswV34A2DxvH4qV85whWTtxoWFFAZ9oRfVhe40922QQr9tqzK5fzEvmI2hU88 2TNw== X-Gm-Message-State: AOJu0Yyn16SdnN6TA71ZGV6wwAgB5yqjor4UOtjS8Vemb4nir6rXJ7JC 0di5B+AO9hJ0n0ucUxqWgQsVjJEEiBs0PBkogod5miNmeWbQ9E9P+KbhvKaZ6ZKRbJdGnYUt3yt 75ACV X-Gm-Gg: ATEYQzzm6iD784JbFEXBSI7kx8c0KR4eEwEtiIjO90a9aMpTTWGbVD3Sp+rdWv/ofev ghIcz4hLCW6C2gUWL+LSpkyK3KOSeeHzJP9lGL8APk7lDVrIhko9jlXNrFKiGdXKQlWTdbtBaH4 giEHop6NwsQPeBuPdPDZbWUNEOA3i4A3LQLuMvd7EdOXG7B7rg9aHYzdNRrUAMTp0+b6osa+MF6 8QvTYqhZLaY/x74gY1FjUE7lZhLKJiiXUQsqK8n7klhgT2K09PTtPhzlAQzfAHuRoNgPD/6JsEX oKZKenWWCQKVbX9sOEnYWk3Vl4GPuZtQst4zhu5b89j3zimf/nBZvsSvml3r5AP8h3BV0+0kB07 RQ19lXEIAvFRp2khOszESZqABHkAatgLDgVsgCeGBibCbPW46Bgi1+6aV7VV1O82b2zLEJWjg4w 5mUSd0bJWPW4kfNb9XHYBlTVLFakMGUREIMbomn9FSd/R0 X-Received: by 2002:a05:600c:3d87:b0:486:5f71:5829 with SMTP id 5b1f17b1804b1-48727d5a307mr258017995e9.5.1774946460702; Tue, 31 Mar 2026 01:41:00 -0700 (PDT) From: Andrew Cooper To: xen-devel@lists.xenproject.org Cc: Andrew Cooper , Jan Beulich , =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= Subject: [PATCH] docs/hypercall-abi: Add a footnote about SYSCALL Date: Tue, 31 Mar 2026 09:40:59 +0100 Message-Id: <20260331084059.20053-1-andrew.cooper3@citrix.com> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-purgate-ID: tlsNG-d25034/1774946462-F4EBB734-3AFC7084/0/0 X-purgate-type: clean X-purgate-size: 1639 X-ZohoMail-DKIM: pass (identity @citrix.com) X-ZM-MESSAGEID: 1774946493974158500 Given that we explicitly support guests making hypercalls without the use of the hypercall page (for CFI and speculative safety reasons), note explicitly that %rcx/%r11 need preserving/clobbering around SYSCALL. Reported-by: Jan Beulich Signed-off-by: Andrew Cooper --- CC: Jan Beulich CC: Roger Pau Monn=C3=A9 I've avoided mentioning FRED seeing as Xen (now) maintains legacy behaviour. --- docs/guest-guide/x86/hypercall-abi.rst | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/docs/guest-guide/x86/hypercall-abi.rst b/docs/guest-guide/x86/= hypercall-abi.rst index e52ed453bcab..ffcf9b1b6d84 100644 --- a/docs/guest-guide/x86/hypercall-abi.rst +++ b/docs/guest-guide/x86/hypercall-abi.rst @@ -62,7 +62,7 @@ between virtualisation mode and hardware vendor. - INT 0x82 =20 * - 64bit PV - - SYSCALL + - SYSCALL [#syscall]_ =20 * - Intel HVM - VMCALL @@ -138,6 +138,10 @@ means. kernel, hypercalls issues from such a mode will be interpreted with the 32bit ABI. Such a setup is not expected in production scenarios. =20 +.. [#syscall] The ``SYSCALL`` instruction modifies ``%rcx`` and ``%r11``. + These registers want spilling or marking as clobbered if invoking the + hypercall without the use of the hypercall page. + .. [#iret] ``HYPERCALL_iret`` is special. It is only implemented for PV guests and takes all its parameters on the stack. This stub should be ``jmp``'d to, rather than ``call``'d. HVM guests have this stub --=20 2.34.1