From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f201.google.com (mail-pg1-f201.google.com [209.85.215.201]) (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 6AA4F29D287 for ; Mon, 11 May 2026 17:48:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778521711; cv=none; b=Kmox43ifUaK/6idj84UWMmqYhA2ej3WiRRbYxFgbog/k/5B0WaCRhv7Aw1wovTGO7mWVrJWw792S3tNhbbOgQqSO5Y1409mCMQQmhFTEfBAYQMFfV1t1Kvrer9Y70RAsUlMEYphg6bGAa5TQuALhOSCUiiiFTBGwbTgnBgGHXaU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778521711; c=relaxed/simple; bh=g0HM4wRy7nS4KwsGK2W4xicmwjdHjeZXsgcIgL8YAH8=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=oq5A8/6tVvv0vsWr3L7/NZySeACH3T9wHHA7pe8oxz737Lu6srBmx1LlZ2/hwqWK62UBDMJjjQR8GpbH3sso8wrpqey+PsnN2hL19yPxxMZ9zy12ejAS0Yfk+OxOLumi0cQeq00nm+LY1YalFXx9WovWeflj5PGCXQblNk3fyg8= 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=JCgSmHO/; arc=none smtp.client-ip=209.85.215.201 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="JCgSmHO/" Received: by mail-pg1-f201.google.com with SMTP id 41be03b00d2f7-c829586e894so498580a12.2 for ; Mon, 11 May 2026 10:48:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1778521710; x=1779126510; darn=vger.kernel.org; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:from:to:cc:subject:date:message-id :reply-to; bh=2zxTSC2plskcs/9y0k8jlg3lj1e2pspt2n223yRFDS4=; b=JCgSmHO/XSQOktpoaSnNH6hPaN5tVFvaoaXgJMiIa8uvRKIbc74RhcNAeLEIPts1r0 Ni8xLFygEF1he4CUMTQ3EbalcWXQEudEriGZYazg5IE69PrplyEc8qTwxALXq75yubxh 7ppCLRdyoFeZjp/4sy/rmEIl6RBONSWjhvQR8BpahbBOO4jwJtjNAEu9OG2x8uwio9re rCGlry23ZEyfR3s9muIvaJjJpAKi5Fyr2FAjVsJo+iz/coytterqOqXbSbLr+E4xM7j0 xRwpiAuvzPsk5BhHUE8L9dX2nkfCcCHmdle5Qw6VkCUifF4pJroBtH//OEcHaiNQhfyM TSPQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1778521710; x=1779126510; h=content-transfer-encoding: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=2zxTSC2plskcs/9y0k8jlg3lj1e2pspt2n223yRFDS4=; b=LmhuF3iY9Ia/EjNZcICRT9gTc9FVECX9PcMaCUB5o2YK6VUMu+WXBkJtbDE1v770GZ sileAcFzPrtxQ/rUJY5RuZCosDdMXkCKYkX4dH0xFhzsleTpqEIIZNzCHMdLYZbPykh9 /ej/Qgq01o6juGAP+f8pfrjisbEUt090/T64ITLzGTMqy09tZqABJlMhwMEJkq+gD/YJ mGosM1O5UZ7hfxNDL+WToew8Nxh2RbmMzuzH+O4rmU9hcNaJV+PPsmDroPMg8eGOFA/U EzBlbnIuVNc4VidVWU7e88q15GC43FZfsqISjAVYcVrqwtkJhcDj/Ps5C84ZI/BtxgY8 Kuyw== X-Forwarded-Encrypted: i=1; AFNElJ+KAoO+DdOSfjCAueSsFxYeefFkbtunUNBa96hsV9GUe5E8qBJLMuHhx1Oz6T1RhG+NibvDnjlTAf9+xFo=@vger.kernel.org X-Gm-Message-State: AOJu0YyHx8eehU9biPDV+bbnxy9xhYgdNsozV4zFwOImtC87OTQlD4v5 JV23BPumrVXW7GxxL1pqiDGkioOQPwTYWhArIzVi5VX08skh4CTgUqdET7I3YcMCCl85dBLku7x +yRTsuw== X-Received: from pfbgh1.prod.google.com ([2002:a05:6a00:6381:b0:82f:2f42:2da4]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:ad0b:b0:82f:74b2:7fba with SMTP id d2e1a72fcca58-83a5b3ca995mr25370247b3a.4.1778521709475; Mon, 11 May 2026 10:48:29 -0700 (PDT) Date: Mon, 11 May 2026 10:48:28 -0700 In-Reply-To: <28709d77abbecdd156c830fbef3c706431d2082a.camel@infradead.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260508181717.3230988-1-dwmw2@infradead.org> <20260508181717.3230988-5-dwmw2@infradead.org> <28709d77abbecdd156c830fbef3c706431d2082a.camel@infradead.org> Message-ID: Subject: Re: [PATCH 4/7] KVM: x86/xen: Remove unnecessary irqsave from GPC lock usage in xen.c From: Sean Christopherson To: David Woodhouse 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 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable 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) us= es > > > read_trylock() instead of read_lock_irqsave(), the remaining GPC lock > > > users in xen.c are only called from process context (vcpu_run, ioctls= ). > > > There is no need to disable interrupts to prevent concurrent access f= rom > > > 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 can= still take the > > lock, but only ever does so using trylock. >=20 > Indeed so. Want me to fix that? Nah, at least not yet. I'm in the process of wrapping my head around all o= f the in-flight gpc series (namely yours and Fred's), just wanted to make sure I = wasn't missing something. Thanks!