On Tue, Dec 12, 2023 at 05:46:34PM +0000, Catalin Marinas wrote: > > diff --git a/include/linux/mm.h b/include/linux/mm.h > > index a422cc123a2d..8d3c4820c492 100644 > > --- a/include/linux/mm.h > > +++ b/include/linux/mm.h > > @@ -391,6 +391,13 @@ extern unsigned int kobjsize(const void *objp); > > # define VM_UFFD_MINOR VM_NONE > > #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */ > > > > +#ifdef CONFIG_64BIT > > +#define VM_VFIO_ALLOW_WC_BIT 39 /* Convey KVM to map S2 NORMAL_NC */ > > This comment shouldn't be in the core header file. It knows nothing > about S2 and Normal-NC, that's arm64 terminology. You can mention > something like VFIO can use this flag hint that write-combining is > allowed. Let's write a comment down here to address both remarks: 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. > should know the implications. There's also an expectation that the > actual driver (KVM guests) or maybe later DPDK can choose the safe > non-cacheable or write-combine (Linux terminology) attributes for the > BAR. DPDK won't rely on this interface Thanks, Jason
