From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f201.google.com (mail-pf1-f201.google.com [209.85.210.201]) (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 5C8EE43634C for ; Mon, 11 May 2026 16:51:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778518270; cv=none; b=Zu6zm+FTGVunj1Mfc/zx+P9cA1bjng8GWl9cMmX5Sym0cxW1aLa9y3Il0e5PYnBklFohzuZd1r2fGuKatim8Y++Js9n9Zi5sKbpurUMenGjnI4iKPI2gino5g0AKImkDKJ/qdmP6XIzUzn1CBnDi7XV38p09089+EwYgw1TUJpI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778518270; c=relaxed/simple; bh=3X4xRBr2112PvEE0OwmnbAt2eKpuQ6Uuwxlk0Ytyvf4=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=Mv/Bcy/jGg9Ul/WvD7TBV9pQE/6gvEkp3HrG4GrqN58WBuuMrUTAKGnOu3x/J0jubLCballJiqbICkfoFRm2/7BFXqSgSaZoN4cualRRWSmtWUuXztXw/7x4cbU2WMZ++w0oYx3H5DaFEBifmQn0WPuWJBA+nHGLAizMmoKAfTw= 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=U6BnKp6h; arc=none smtp.client-ip=209.85.210.201 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="U6BnKp6h" Received: by mail-pf1-f201.google.com with SMTP id d2e1a72fcca58-837cc5bc6deso3086572b3a.3 for ; Mon, 11 May 2026 09:51:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1778518269; x=1779123069; 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=Iom8ndLx++CwN+appoNm2rlIoGdhrDtcVkMkfINFBqs=; b=U6BnKp6hyngpUypeo8HgytUJ9HjrQOt2a04IqipLTE3m9roiLaIefJVGbgtRPYpUOU 4+JO0BdJpTc8I7pseyDmaQD0gD18XcsgLMIOyApntlNRjWZ46kJktGjE66GPh0olIqCR adVlYjXNgoHR78G/9k0B3y5G7ts3NFjxQXBNKwQWCBANbxBL7JiZ0ZE41kePMxVK1tDf U3ljs4jfKGSaLs4XqEDOmFecNaQ5KQVnl83KW/MWpA3fGIoT/X2g5iHxZKNF6vQO3JJH bUJTBaVHX5/E/SgyeL+D8drN08OeTH0+vXGT0OA2/poRzl1p/BBr+bS2Ko1e4nZ6FyqQ YByQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1778518269; x=1779123069; 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=Iom8ndLx++CwN+appoNm2rlIoGdhrDtcVkMkfINFBqs=; b=MRgDQlteUHtWlJxrL/8gPf4l4QoNLpJC2vfEnkXzntuOz7XH7LulrAJUYjFnS4FJhw BwvCzmKu8vOBI75XJXJ2U0ZICjVix77pRJ6/pFh/mAn4ff4aN8u+bPBUkKQ0Qbmu5lHi Db9SKfJLExFwcYAvOTDJwrEYLNxAmnsJfCimkF1OLAOOF6HL13C9tI/CDFP9zuTrSAGX LHIxWEBkRlUN8hY6e4MktdNFMxHGWbrEnUm00kx70C1CRoJGBZVgBcpP36OrqDlxaj2J BIjUM1XGhXzUuoFih06uz8IgilO7Gjn7u1cYgJFBfueorFrfm2x6/Zh9p/njjzGzijFE crPQ== X-Forwarded-Encrypted: i=1; AFNElJ+MAqfTJwHxsr+YXfpL7QUPUhFWh/ppZbIy6tDggbjfcV2WLh97mXyXdORToSOPCf/fN4A99XIWaOmhmww=@vger.kernel.org X-Gm-Message-State: AOJu0YwbHEp+OfOky6iRpKra1qDsTaoWE3KjEmcU6joHXfSgxedjBPuk EC0axBFVSElXuTngK+tW8D7y95xY9J41Gr6oqb5TYBFoOMIv83dneg0QYCb7/0sJw9KTBXQA7qZ M2DJMyA== 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:a05:6a00:3013:b0:838:3404:c2b0 with SMTP id d2e1a72fcca58-83a5b8d9aaemr23075127b3a.13.1778518268359; Mon, 11 May 2026 09:51:08 -0700 (PDT) Date: Mon, 11 May 2026 09:51:07 -0700 In-Reply-To: <20260508181717.3230988-5-dwmw2@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> 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="us-ascii" On Fri, May 08, 2026, David Woodhouse wrote: > From: David Woodhouse > > Now that the hardirq path (xen_timer_callback and set_evtchn_fast) uses > 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 from > a hardirq user, since the hardirq path no longer takes the lock. No longer _waits_ on the lock, correct? I.e. the hardirq path can still take the lock, but only ever does so using trylock.