From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To: Shanker Donthineni <sdonthineni@nvidia.com>
Cc: Marc Zyngier <maz@kernel.org>,
Alex Williamson <alex.williamson@redhat.com>,
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>,
Jason Sequeira <jsequeira@nvidia.com>,
jgg@nvidia.com, benh@kernel.crashing.org
Subject: Re: [RFC 1/2] vfio/pci: keep the prefetchable attribute of a BAR region in VMA
Date: Fri, 30 Apr 2021 10:54:17 +0100 [thread overview]
Message-ID: <20210430095417.GA13686@lpieralisi> (raw)
In-Reply-To: <20210429162906.32742-2-sdonthineni@nvidia.com>
[+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 <sdonthineni@nvidia.com>
> ---
> 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
>
next prev parent reply other threads:[~2021-04-30 9:54 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-29 16:29 [RFC 0/2] [RFC] Honor PCI prefetchable attributes for a virtual machine on ARM64 Shanker Donthineni
2021-04-29 16:29 ` [RFC 1/2] vfio/pci: keep the prefetchable attribute of a BAR region in VMA Shanker Donthineni
2021-04-29 18:28 ` Alex Williamson
2021-04-29 19:14 ` Shanker R Donthineni
2021-04-29 19:46 ` Alex Williamson
2021-04-29 22:08 ` Vikram Sethi
2021-04-30 11:25 ` Shanker R Donthineni
[not found] ` <87czucngdc.wl-maz@kernel.org>
2021-04-30 13:07 ` Shanker R Donthineni
2021-04-30 14:58 ` Shanker R Donthineni
[not found] ` <878s4zokll.wl-maz@kernel.org>
2021-04-30 16:57 ` Vikram Sethi
2021-05-01 9:30 ` Marc Zyngier
2021-05-01 11:36 ` Shanker R Donthineni
[not found] ` <87czu8uowe.wl-maz@kernel.org>
2021-05-03 12:08 ` Shanker R Donthineni
2021-05-02 17:56 ` Vikram Sethi
2021-05-03 10:17 ` Marc Zyngier
2021-05-03 13:35 ` Mark Kettenis
2021-05-03 13:59 ` Vikram Sethi
2021-05-03 14:44 ` Alex Williamson
2021-05-03 22:03 ` Vikram Sethi
2021-05-04 8:30 ` Will Deacon
2021-05-05 18:02 ` Catalin Marinas
2021-05-06 7:22 ` Christoph Hellwig
2021-05-08 16:33 ` Shanker R Donthineni
2021-06-02 9:37 ` Marc Zyngier
2021-05-04 18:03 ` Alex Williamson
2021-06-02 9:11 ` Marc Zyngier
2021-04-30 9:54 ` Lorenzo Pieralisi [this message]
2021-04-30 12:38 ` Jason Gunthorpe
2021-04-29 16:29 ` [RFC 2/2] KVM: arm64: Add write-combine support for stage-2 entries Shanker Donthineni
2021-05-03 7:01 ` [RFC 0/2] [RFC] Honor PCI prefetchable attributes for a virtual machine on ARM64 Christoph Hellwig
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