From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2F2C429D287; Mon, 11 May 2026 18:12:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778523174; cv=none; b=orbc+I68V/itDY44WJjju6sbn0fGLfhcN+643aEBFnvEJUFVQS1J1ao1Xs65/MMmfsTHpqt87VKShOj3+Z8IxPKySXRAt5xBXLFweanJNmN9agArUVYO+M1XO2MeVi3UOIO3f6jmfQrJafLUMBVtsiUE5MGJG5nWs9o7GNCAoQQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778523174; c=relaxed/simple; bh=7CKwJxI3bFLm3PFuh9AaFsTZTrTKlPGrPO8xNlZ51xA=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=IGy2raaSz2m7bu+wjtEz8Hz765rPooY5FssYoJ9s6kkHzYr/P9L/7SwqVT5+X/mjZ0kJZATLTUjCRq/m1IKpfFD0cz/qBK6FuST0k65WrnCa/7kLq+2hUxPgaW8sJ+b1EP4MctjMwkjVmMHgF0F1EZhNkpKv+WxEjBhllNBjyGk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=casper.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=dzRWjlmj; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=casper.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="dzRWjlmj" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=7CKwJxI3bFLm3PFuh9AaFsTZTrTKlPGrPO8xNlZ51xA=; b=dzRWjlmj2KmbQuiyCKcsh6RceF kcbEiOSX3NxMRfU9rbYVG/uuULEPj/xowMa/YSyMmjB3vyBZH549WFyce/jvR3LMtW7VVCe7JzhQi ogM9DY2YhM6WgXaLyfU90yuJLt2r8bJsdKGy2Wv+vAAA+hGUbfpRwXmOJep7lGgfGNsNbg+iNpmbR ptjoyEv7VY5nK25EQZ0XGv1R4VmD2re928LiN7lT/XhjmVMTkMtuxVd+htcQcakfzuTF8XF3lt84B kurwj9CTiCIMUFOUfPUI7D1117mrcxeYhvayMVIkR8KpilPZh2mrig3Y9vMyBtxywVFjsOSvT0t5S KupScbkQ==; Received: from 54-240-197-239.amazon.com ([54.240.197.239] helo=edge-cache-179.e-lhr50.amazon.com) by casper.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1wMV7P-00000008ady-0Mnz; Mon, 11 May 2026 18:12:39 +0000 Message-ID: <177d33b213c71c965da8ccf43f042264656dc99d.camel@infradead.org> Subject: Re: [PATCH 4/7] KVM: x86/xen: Remove unnecessary irqsave from GPC lock usage in xen.c From: David Woodhouse To: Sean Christopherson , "Griffoul, Fred" Cc: Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Paul Durrant , Peter Zijlstra , Will Deacon , Boqun Feng , Waiman Long , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, Mauricio Faria de Oliveira , kernel-dev@igalia.com, syzbot+208f7f3e5f59c11aeb90@syzkaller.appspotmail.com Date: Mon, 11 May 2026 19:12:37 +0100 In-Reply-To: References: <20260508181717.3230988-1-dwmw2@infradead.org> <20260508181717.3230988-5-dwmw2@infradead.org> <28709d77abbecdd156c830fbef3c706431d2082a.camel@infradead.org> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-HzePcSBQrEs8fgoH568w" User-Agent: Evolution 3.52.3-0ubuntu1.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html --=-HzePcSBQrEs8fgoH568w Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2026-05-11 at 10:48 -0700, Sean Christopherson wrote: > On Mon, May 11, 2026, David Woodhouse wrote: > > On Mon, 2026-05-11 at 09:51 -0700, Sean Christopherson wrote: > > > On Fri, May 08, 2026, David Woodhouse wrote: > > > > From: David Woodhouse > > > >=20 > > > > Now that the hardirq path (xen_timer_callback and set_evtchn_fast) = uses > > > > read_trylock() instead of read_lock_irqsave(), the remaining GPC lo= ck > > > > users in xen.c are only called from process context (vcpu_run, ioct= ls). > > > > There is no need to disable interrupts to prevent concurrent access= from > > > > a hardirq user, since the hardirq path no longer takes the lock. > > >=20 > > > No longer _waits_ on the lock, correct?=C2=A0 I.e. the hardirq path c= an still take the > > > lock, but only ever does so using trylock. > >=20 > > Indeed so. Want me to fix that? >=20 > Nah, at least not yet.=C2=A0 I'm in the process of wrapping my head aroun= d all of the > in-flight gpc series (namely yours and Fred's), just wanted to make sure = I wasn't > missing something. I think Fred has a few performance fixes and is due to send another version once he can find the cycles to do so. My assumption (without actually *talking* to Fred about it) was that he would be able to rebase fairly trivially on top of this series. --=-HzePcSBQrEs8fgoH568w Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCD9Aw ggSOMIIDdqADAgECAhAOmiw0ECVD4cWj5DqVrT9PMA0GCSqGSIb3DQEBCwUAMGUxCzAJBgNVBAYT AlVTMRUwEwYDVQQKEwxEaWdpQ2VydCBJbmMxGTAXBgNVBAsTEHd3dy5kaWdpY2VydC5jb20xJDAi BgNVBAMTG0RpZ2lDZXJ0IEFzc3VyZWQgSUQgUm9vdCBDQTAeFw0yNDAxMzAwMDAwMDBaFw0zMTEx MDkyMzU5NTlaMEExCzAJBgNVBAYTAkFVMRAwDgYDVQQKEwdWZXJva2V5MSAwHgYDVQQDExdWZXJv a2V5IFNlY3VyZSBFbWFpbCBHMjCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMjvgLKj jfhCFqxYyRiW8g3cNFAvltDbK5AzcOaR7yVzVGadr4YcCVxjKrEJOgi7WEOH8rUgCNB5cTD8N/Et GfZI+LGqSv0YtNa54T9D1AWJy08ZKkWvfGGIXN9UFAPMJ6OLLH/UUEgFa+7KlrEvMUupDFGnnR06 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