| Message ID | 20240211174705.31992-3-ankita@nvidia.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | kvm: arm64: allow the VM to select DEVICE_* and NORMAL_NC for IO memory | expand |
On 11.02.24 18:47, ankita@nvidia.com wrote: > From: Ankit Agrawal <ankita@nvidia.com> > > Generalizing S2 setting from DEVICE_nGnRE to NormalNc for non PCI > devices may be problematic. E.g. GICv2 vCPU interface, which is > effectively a shared peripheral, can allow a guest to affect another > guest's interrupt distribution. The issue may be solved by limiting > the relaxation to mappings that have a user VMA. Still there is > insufficient information and uncertainity in the behavior of s/uncertainity/uncertainty/ > non PCI drivers. > > Add a new flag VM_ALLOW_ANY_UNCACHED to indicate KVM that the device > is WC capable and these S2 changes can be extended to it. KVM can use > this flag to activate the code. > MM people will stumble only over this commit at some point, looking for details. It might make sense to add a bit more details on the underlying problem (user space tables vs. stage-1 vs. stage-2) and why we want to have a different mapping in user space compared to stage-1. Then, describe that the VMA flag was found to be the simplest and cleanest way to communicate this information from VFIO to KVM. > Suggested-by: Catalin Marinas <catalin.marinas@arm.com> > Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> > Signed-off-by: Ankit Agrawal <ankita@nvidia.com> > --- > include/linux/mm.h | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index f5a97dec5169..59576e56c58b 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -391,6 +391,20 @@ extern unsigned int kobjsize(const void *objp); > # define VM_UFFD_MINOR VM_NONE > #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */ > > +/* > + * This flag is used to connect VFIO to arch specific KVM code. It > + * indicates that the memory under this VMA is safe for use with any > + * non-cachable memory type inside KVM. Some VFIO devices, on some > + * platforms, are thought to be unsafe and can cause machine crashes > + * if KVM does not lock down the memory type. > + */ > +#ifdef CONFIG_64BIT > +#define VM_ALLOW_ANY_UNCACHED_BIT 39 > +#define VM_ALLOW_ANY_UNCACHED BIT(VM_ALLOW_ANY_UNCACHED_BIT) > +#else > +#define VM_ALLOW_ANY_UNCACHED VM_NONE > +#endif > + > /* Bits set in the VMA until the stack is in its final location */ > #define VM_STACK_INCOMPLETE_SETUP (VM_RAND_READ | VM_SEQ_READ | VM_STACK_EARLY) > It's not perfect (very VFIO <-> KVM specific right now, VMA flags feel a bit wrong), but it certainly easier and cleaner than any alternatives I could think of. Acked-by: David Hildenbrand <david@redhat.com>
>> insufficient information and uncertainity in the behavior of > > s/uncertainity/uncertainty/ Ack. >> non PCI drivers. >> >> Add a new flag VM_ALLOW_ANY_UNCACHED to indicate KVM that the device >> is WC capable and these S2 changes can be extended to it. KVM can use >> this flag to activate the code. >> > > MM people will stumble only over this commit at some point, looking for > details. It might make sense to add a bit more details on the underlying > problem (user space tables vs. stage-1 vs. stage-2) and why we want to > have a different mapping in user space compared to stage-1. > > Then, describe that the VMA flag was found to be the simplest and > cleanest way to communicate this information from VFIO to KVM. Okay, I'll work on the commit message and describe in more details in the next version. >> +/* >> + * This flag is used to connect VFIO to arch specific KVM code. It >> + * indicates that the memory under this VMA is safe for use with any >> + * non-cachable memory type inside KVM. Some VFIO devices, on some >> + * platforms, are thought to be unsafe and can cause machine crashes >> + * if KVM does not lock down the memory type. >> + */ >> +#ifdef CONFIG_64BIT >> +#define VM_ALLOW_ANY_UNCACHED_BIT 39 >> +#define VM_ALLOW_ANY_UNCACHED BIT(VM_ALLOW_ANY_UNCACHED_BIT) >> +#else >> +#define VM_ALLOW_ANY_UNCACHED VM_NONE >> +#endif >> + >> /* Bits set in the VMA until the stack is in its final location */ >> #define VM_STACK_INCOMPLETE_SETUP (VM_RAND_READ | VM_SEQ_READ | VM_STACK_EARLY) >> > > It's not perfect (very VFIO <-> KVM specific right now, VMA flags feel a > bit wrong), but it certainly easier and cleaner than any alternatives I > could think of. > > Acked-by: David Hildenbrand <david@redhat.com> Thanks! FWIW, it was found the cleanest way to restrict the changes to vfio-pci.
diff --git a/include/linux/mm.h b/include/linux/mm.h index f5a97dec5169..59576e56c58b 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -391,6 +391,20 @@ extern unsigned int kobjsize(const void *objp); # define VM_UFFD_MINOR VM_NONE #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */ +/* + * This flag is used to connect VFIO to arch specific KVM code. It + * indicates that the memory under this VMA is safe for use with any + * non-cachable memory type inside KVM. Some VFIO devices, on some + * platforms, are thought to be unsafe and can cause machine crashes + * if KVM does not lock down the memory type. + */ +#ifdef CONFIG_64BIT +#define VM_ALLOW_ANY_UNCACHED_BIT 39 +#define VM_ALLOW_ANY_UNCACHED BIT(VM_ALLOW_ANY_UNCACHED_BIT) +#else +#define VM_ALLOW_ANY_UNCACHED VM_NONE +#endif + /* Bits set in the VMA until the stack is in its final location */ #define VM_STACK_INCOMPLETE_SETUP (VM_RAND_READ | VM_SEQ_READ | VM_STACK_EARLY)