Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Received-SPF: Pass (protection.outlook.com: domain of nvidia.com designates
 216.228.112.34 as permitted sender) receiver=protection.outlook.com;
 client-ip=216.228.112.34; helo=mail.nvidia.com;
From:   Shanker Donthineni <sdonthineni@nvidia.com>
To:     Marc Zyngier <maz@kernel.org>,
        Alex Williamson <alex.williamson@redhat.com>
CC:     Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Christoffer Dall <christoffer.dall@arm.com>,
        <linux-arm-kernel@lists.infradead.org>,
        <kvmarm@lists.cs.columbia.edu>, <linux-kernel@vger.kernel.org>,
        <kvm@vger.kernel.org>, Vikram Sethi <vsethi@nvidia.com>,
        Shanker Donthineni <sdonthineni@nvidia.com>,
        "Jason Sequeira" <jsequeira@nvidia.com>
Subject: [RFC 1/2] vfio/pci: keep the prefetchable attribute of a BAR region in VMA
Date:   Thu, 29 Apr 2021 11:29:05 -0500
Message-ID: <20210429162906.32742-2-sdonthineni@nvidia.com>
In-Reply-To: <20210429162906.32742-1-sdonthineni@nvidia.com>
References: <20210429162906.32742-1-sdonthineni@nvidia.com>
MIME-Version: 1.0
Content-Type: text/plain
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 29 Apr 2021 16:29:49.4348
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: 9a05a37d-ff50-4df9-2514-08d90b2c0257
X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.112.34];Helo=[mail.nvidia.com]
X-MS-Exchange-CrossTenant-AuthSource: DM6NAM11FT015.eop-nam11.prod.protection.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Anonymous
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR12MB3279
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

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 <sdonthineni@nvidia.com>
---
 drivers/vfio/pci/vfio_pci.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

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