From: Alex Williamson <alex.williamson@redhat.com> To: Jason Gunthorpe <jgg@nvidia.com> Cc: ankita@nvidia.com, maz@kernel.org, oliver.upton@linux.dev, james.morse@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, reinette.chatre@intel.com, surenb@google.com, stefanha@redhat.com, brauner@kernel.org, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, kevin.tian@intel.com, yi.l.liu@intel.com, ardb@kernel.org, akpm@linux-foundation.org, andreyknvl@gmail.com, wangjinchao@xfusion.com, gshan@redhat.com, shahuang@redhat.com, ricarkol@google.com, linux-mm@kvack.org, lpieralisi@kernel.org, rananta@google.com, ryan.roberts@arm.com, david@redhat.com, linus.walleij@linaro.org, bhe@redhat.com, aniketa@nvidia.com, cjia@nvidia.com, kwankhede@nvidia.com, targupta@nvidia.com, vsethi@nvidia.com, acurrid@nvidia.com, apopple@nvidia.com, jhubbard@nvidia.com, danw@nvidia.com, kvmarm@lists.linux.dev, mochs@nvidia.com, zhiw@nvidia.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v7 4/4] vfio: convey kvm that the vfio-pci device is wc safe Date: Mon, 12 Feb 2024 10:27:18 -0700 [thread overview] Message-ID: <20240212102718.07543659.alex.williamson@redhat.com> (raw) In-Reply-To: <20240212172001.GE4048826@nvidia.com> On Mon, 12 Feb 2024 13:20:01 -0400 Jason Gunthorpe <jgg@nvidia.com> wrote: > On Mon, Feb 12, 2024 at 10:05:02AM -0700, Alex Williamson wrote: > > > > --- 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. > > Sure, if you want to elaborate more > > The VM_ALLOW_ANY_UNCACHED flag is implemented for ARM64, > allowing KVM stage 2 device mapping attributes to use Normal-NC > rather than DEVICE_nGnRE, which allows guest mappings > supporting combining attributes (WC). ARM does not architecturally > guarentee this is safe, and indeed some MMIO regions like the GICv2 > VCPU interface can trigger uncontained faults if Normal-NC is used. > > Even worse we expect there are platforms where even DEVICE_nGnRE can > allow uncontained faults in conercases. Unfortunately existing ARM ^^^^^^^^^^ *corner cases > IP requires platform integration to take responsibility to prevent > this. > > To safely use VFIO in KVM the platform must guarantee full safety > in the guest where no action taken against a MMIO mapping can > trigger an uncontainer failure. We belive that most VFIO PCI > platforms support this for both mapping types, at least in common > flows, based on some expectations of how PCI IP is integrated. This > can be enabled more broadly, for instance into vfio-platform > drivers, but only after the platform vendor completes auditing for > safety. I like it, please incorporate into the next version. > > 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? > > Maybe more like "we have a general consensus that vfio-pci is likely > safe due to how PCI IP is typically integrated, but it is much less > obvious for other VFIO bus types. As there is no known WC user for > vfio-platform drivers be conservative and do not enable it." Ok. Thanks for the clarification. Alex
WARNING: multiple messages have this Message-ID (diff)
From: Alex Williamson <alex.williamson@redhat.com> To: Jason Gunthorpe <jgg@nvidia.com> Cc: ankita@nvidia.com, maz@kernel.org, oliver.upton@linux.dev, james.morse@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, reinette.chatre@intel.com, surenb@google.com, stefanha@redhat.com, brauner@kernel.org, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, kevin.tian@intel.com, yi.l.liu@intel.com, ardb@kernel.org, akpm@linux-foundation.org, andreyknvl@gmail.com, wangjinchao@xfusion.com, gshan@redhat.com, shahuang@redhat.com, ricarkol@google.com, linux-mm@kvack.org, lpieralisi@kernel.org, rananta@google.com, ryan.roberts@arm.com, david@redhat.com, linus.walleij@linaro.org, bhe@redhat.com, aniketa@nvidia.com, cjia@nvidia.com, kwankhede@nvidia.com, targupta@nvidia.com, vsethi@nvidia.com, acurrid@nvidia.com, apopple@nvidia.com, jhubbard@nvidia.com, danw@nvidia.com, kvmarm@lists.linux.dev, mochs@nvidia.com, zhiw@nvidia.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v7 4/4] vfio: convey kvm that the vfio-pci device is wc safe Date: Mon, 12 Feb 2024 10:27:18 -0700 [thread overview] Message-ID: <20240212102718.07543659.alex.williamson@redhat.com> (raw) In-Reply-To: <20240212172001.GE4048826@nvidia.com> On Mon, 12 Feb 2024 13:20:01 -0400 Jason Gunthorpe <jgg@nvidia.com> wrote: > On Mon, Feb 12, 2024 at 10:05:02AM -0700, Alex Williamson wrote: > > > > --- 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. > > Sure, if you want to elaborate more > > The VM_ALLOW_ANY_UNCACHED flag is implemented for ARM64, > allowing KVM stage 2 device mapping attributes to use Normal-NC > rather than DEVICE_nGnRE, which allows guest mappings > supporting combining attributes (WC). ARM does not architecturally > guarentee this is safe, and indeed some MMIO regions like the GICv2 > VCPU interface can trigger uncontained faults if Normal-NC is used. > > Even worse we expect there are platforms where even DEVICE_nGnRE can > allow uncontained faults in conercases. Unfortunately existing ARM ^^^^^^^^^^ *corner cases > IP requires platform integration to take responsibility to prevent > this. > > To safely use VFIO in KVM the platform must guarantee full safety > in the guest where no action taken against a MMIO mapping can > trigger an uncontainer failure. We belive that most VFIO PCI > platforms support this for both mapping types, at least in common > flows, based on some expectations of how PCI IP is integrated. This > can be enabled more broadly, for instance into vfio-platform > drivers, but only after the platform vendor completes auditing for > safety. I like it, please incorporate into the next version. > > 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? > > Maybe more like "we have a general consensus that vfio-pci is likely > safe due to how PCI IP is typically integrated, but it is much less > obvious for other VFIO bus types. As there is no known WC user for > vfio-platform drivers be conservative and do not enable it." Ok. Thanks for the clarification. Alex _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2024-02-12 17:27 UTC|newest] Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-02-11 17:47 [PATCH v7 0/4] kvm: arm64: allow the VM to select DEVICE_* and NORMAL_NC for IO memory ankita 2024-02-11 17:47 ` ankita 2024-02-11 17:47 ` [PATCH v7 1/4] kvm: arm64: introduce new flag for non-cacheable " ankita 2024-02-11 17:47 ` ankita 2024-02-11 17:47 ` [PATCH v7 2/4] mm: introduce new flag to indicate wc safe ankita 2024-02-11 17:47 ` ankita 2024-02-12 13:13 ` David Hildenbrand 2024-02-12 13:13 ` David Hildenbrand 2024-02-13 3:41 ` Ankit Agrawal 2024-02-13 3:41 ` Ankit Agrawal 2024-02-11 17:47 ` [PATCH v7 3/4] kvm: arm64: set io memory s2 pte as normalnc for vfio pci device ankita 2024-02-11 17:47 ` ankita 2024-02-11 17:47 ` [PATCH v7 4/4] vfio: convey kvm that the vfio-pci device is wc safe ankita 2024-02-11 17:47 ` ankita 2024-02-12 13:16 ` David Hildenbrand 2024-02-12 13:16 ` David Hildenbrand 2024-02-12 17:05 ` Alex Williamson 2024-02-12 17:05 ` Alex Williamson 2024-02-12 17:20 ` Jason Gunthorpe 2024-02-12 17:20 ` Jason Gunthorpe 2024-02-12 17:27 ` Alex Williamson [this message] 2024-02-12 17:27 ` Alex Williamson 2024-02-13 1:59 ` Ankit Agrawal 2024-02-13 1:59 ` Ankit Agrawal 2024-02-12 10:26 ` [PATCH v7 0/4] kvm: arm64: allow the VM to select DEVICE_* and NORMAL_NC for IO memory David Hildenbrand 2024-02-12 10:26 ` David Hildenbrand 2024-02-12 12:56 ` Jason Gunthorpe 2024-02-12 12:56 ` Jason Gunthorpe 2024-02-12 13:06 ` David Hildenbrand 2024-02-12 13:06 ` David Hildenbrand 2024-02-12 20:24 ` Oliver Upton 2024-02-12 20:24 ` Oliver Upton 2024-02-13 2:29 ` Ankit Agrawal 2024-02-13 2:29 ` Ankit Agrawal
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