From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 772295381B for ; Thu, 15 Aug 2024 05:05:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723698309; cv=none; b=giaxhBLKGg7cFguABG2XUbkbJbPuD4Z6PwukjTLoYvsGh7GBl2G6kooKZ10NXj710K37BTXBNh8dg6Z0WAAbNIOp6k/XvFza1bqx+3sxa3JlCnZXL7R0fryQ5Alv8Nq4IBVr6mTpa7vLDMeyajUX9WZKjtX39T5pMxMLySBNX9s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723698309; c=relaxed/simple; bh=PA5Hwj+tfgC6UoZCE/5fxSQR+GLHW6h7nA1pX+OUEMY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=E5RFrbp1CokTW3b+Iu3zWIIyNlq0njAqJG2rbVeSS3FkBia7uneLYikDO9Z+fWuonESNiN3ZR83V1kvQq3WE+C5YcFvP4ITDCw14A2wAAqCHpTJW1sgELpB6/658kZ6r12B6AT9DWYvogBpJIiKDbR4hfsB+7UPrbFd/38hLMDs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=Ae/UEYWx; arc=none smtp.client-ip=198.137.202.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Ae/UEYWx" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=5H163FAIJf+dNKAeDC1P4tskQtErqFRv7CGKy1izrqo=; b=Ae/UEYWx+pwHkeXMkJ8fj3eNZv QBsNGhjI7ErsjKR4IAR7mX3X4B/zUpfphe1eUaa2ysLZoFz2ZtJZ0fsPGCRLMbvJ/NDc6lCsRjrBY xVw+O0S0oHOnvk79zBtNSBONi+FiJPwNjaQYhb7XOCtCnugy2ShPQGVm2d7PFOTczVOO8876MX9UH P0uU01+PbXqQvaMeWOMgiDfkCj3jQMV4OIjKH/tRXGHD/l9XOW6JKZ/21JBGi2xKO7yvis3qnzex6 TTMNormUxWvW1Pq9j22oedeWUDzMLt4/Jna8F7XKjZlBzLuVqYsJRl98bFu1VYTsUHiNfW5YS/xPE J7YjG10A==; Received: from hch by bombadil.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1seSfa-000000092Bh-0wzn; Thu, 15 Aug 2024 05:05:06 +0000 Date: Wed, 14 Aug 2024 22:05:06 -0700 From: Christoph Hellwig To: Keith Busch Cc: Alex Williamson , Jason Gunthorpe , Keith Busch , kvm@vger.kernel.org Subject: Re: [PATCH rfc] vfio-pci: Allow write combining Message-ID: References: <20240731155352.3973857-1-kbusch@meta.com> <20240801141914.GC3030761@ziepe.ca> <20240801094123.4eda2e91.alex.williamson@redhat.com> <20240801161130.GD3030761@ziepe.ca> <20240801105218.7c297f9a.alex.williamson@redhat.com> <20240801171355.GA4830@ziepe.ca> <20240801113344.1d5b5bfe.alex.williamson@redhat.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html On Fri, Aug 02, 2024 at 08:24:49AM -0600, Keith Busch wrote: > Which itself follows the existing pattern from > pci_create_resource_files(), which creates a write combine > resource_wc file only when IORESOURCE_PREFETCH is set. But yeah, > prefetch isn't necessary for wc, but it seems to indicate it's safe. Apparently IORESOURCE_PREFETCH never implied anything about write combinability, and Linux got this wrong long time ago. The fact that we do this now clashes with PCI SIGs desire to kill the concept of prefetcable BARs that they are forcing down everyones throat.