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Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1lcPqv-001HrP-UX for linux-arm-kernel@lists.infradead.org; Fri, 30 Apr 2021 09:54:31 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id C087031B; Fri, 30 Apr 2021 02:54:24 -0700 (PDT) Received: from lpieralisi (e121166-lin.cambridge.arm.com [10.1.196.255]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 01C143F73B; Fri, 30 Apr 2021 02:54:22 -0700 (PDT) Date: Fri, 30 Apr 2021 10:54:17 +0100 From: Lorenzo Pieralisi To: Shanker Donthineni Cc: Marc Zyngier , Alex Williamson , Will Deacon , Catalin Marinas , Christoffer Dall , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Vikram Sethi , Jason Sequeira , jgg@nvidia.com, benh@kernel.crashing.org Subject: Re: [RFC 1/2] vfio/pci: keep the prefetchable attribute of a BAR region in VMA Message-ID: <20210430095417.GA13686@lpieralisi> References: <20210429162906.32742-1-sdonthineni@nvidia.com> <20210429162906.32742-2-sdonthineni@nvidia.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210429162906.32742-2-sdonthineni@nvidia.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210430_025430_052425_FEBA1A20 X-CRM114-Status: GOOD ( 18.87 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org [+Jason, Ben] On Thu, Apr 29, 2021 at 11:29:05AM -0500, Shanker Donthineni wrote: > For pass-through device assignment, the ARM64 KVM hypervisor retrieves > the memory region properties physical address, size, and whether a > region backed with struct page or not from VMA. The prefetchable > attribute of a BAR region isn't visible to KVM to make an optimal > decision for stage2 attributes. > > This patch updates vma->vm_page_prot and maps with write-combine > attribute if the associated BAR is prefetchable. For ARM64 > pgprot_writecombine() is mapped to memory-type MT_NORMAL_NC which > has no side effects on reads and multiple writes can be combined. > > Signed-off-by: Shanker Donthineni > --- > drivers/vfio/pci/vfio_pci.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) A bit of background information that may be useful: https://lore.kernel.org/linux-pci/2b539df4c9ec703458e46da2fc879ee3b310b31c.camel@kernel.crashing.org Lorenzo > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c > index 5023e23db3bc..1b734fe1dd51 100644 > --- a/drivers/vfio/pci/vfio_pci.c > +++ b/drivers/vfio/pci/vfio_pci.c > @@ -1703,7 +1703,11 @@ static int vfio_pci_mmap(void *device_data, struct vm_area_struct *vma) > } > > vma->vm_private_data = vdev; > - vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); > + if (IS_ENABLED(CONFIG_ARM64) && > + (pci_resource_flags(pdev, index) & IORESOURCE_PREFETCH)) > + vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot); > + else > + vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); > vma->vm_pgoff = (pci_resource_start(pdev, index) >> PAGE_SHIFT) + pgoff; > > /* > -- > 2.17.1 > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel