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Mon, 12 Feb 2024 09:05:04 -0800 (PST) Date: Mon, 12 Feb 2024 10:05:02 -0700 From: Alex Williamson To: Cc: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v7 4/4] vfio: convey kvm that the vfio-pci device is wc safe Message-ID: <20240212100502.2b5009e4.alex.williamson@redhat.com> In-Reply-To: <20240211174705.31992-5-ankita@nvidia.com> References: <20240211174705.31992-1-ankita@nvidia.com> <20240211174705.31992-5-ankita@nvidia.com> X-Mailer: Claws Mail 4.2.0 (GTK 3.24.38; x86_64-redhat-linux-gnu) MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: C60CDC0028 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: dr7gri3s9xhpxa7bpjw4bfhecm5ckxdg X-HE-Tag: 1707757508-759700 X-HE-Meta: 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 uquPUVks J7XhJ41yESU067bZEzXsNki2BtbqVQZthClcQzFHZB0hpso9IIRoLRKW1FBteTOHpsCt3xaYKgcN1bOWBV1nbTycLV9WJpwL5Xtm5 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, 11 Feb 2024 23:17:05 +0530 wrote: > From: Ankit Agrawal > > The code to map the MMIO in S2 as NormalNC is enabled when conveyed > that the device is WC safe using a new flag VM_ALLOW_ANY_UNCACHED. > > Make vfio-pci set the VM_ALLOW_ANY_UNCACHED flag. > > This could be extended to other devices in the future once that > is deemed safe. > > Suggested-by: Catalin Marinas > Acked-by: Jason Gunthorpe > Acked-by: Catalin Marinas > Signed-off-by: Ankit Agrawal > --- > drivers/vfio/pci/vfio_pci_core.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c > index 1cbc990d42e0..eba2146202f9 100644 > --- a/drivers/vfio/pci/vfio_pci_core.c > +++ b/drivers/vfio/pci/vfio_pci_core.c > @@ -1862,8 +1862,12 @@ int vfio_pci_core_mmap(struct vfio_device *core_vdev, struct vm_area_struct *vma > /* > * See remap_pfn_range(), called from vfio_pci_fault() but we can't > * change vm_flags within the fault handler. Set them now. > + * > + * Set an additional flag VM_ALLOW_ANY_UNCACHED to convey kvm that > + * the device is wc safe. > */ That's a pretty superficial comment. Check that this is accurate, but maybe something like: The VM_ALLOW_ANY_UNCACHED flag is implemented for ARM64, allowing stage 2 device mapping attributes to use Normal-NC rather than DEVICE_nGnRE, which allows guest mappings supporting combining attributes (WC). This attribute has potential risks with the GICv2 VCPU interface, but is expected to be safe for vfio-pci use cases. And specifically, I think these other devices that may be problematic as described in the cover letter is a warning against use for vfio-platform, is that correct? Thanks, Alex > - vm_flags_set(vma, VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP); > + vm_flags_set(vma, VM_ALLOW_ANY_UNCACHED | VM_IO | VM_PFNMAP | > + VM_DONTEXPAND | VM_DONTDUMP); > vma->vm_ops = &vfio_pci_mmap_ops; > > return 0;