Hi Christoffer, On 01/06/17 23:22, Christoffer Dall wrote: > On Wed, May 24, 2017 at 05:32:50PM +0100, James Morse wrote: >> Once we enable ARCH_SUPPORTS_MEMORY_FAILURE on arm64, notifications for >> broken memory can call memory_failure() in mm/memory-failure.c to deliver >> SIGBUS to any user space process using the page, and notify all the >> in-kernel users. >> >> If the page corresponded with guest memory, KVM will unmap this page >> from its stage2 page tables. The user space process that allocated >> this memory may have never touched this page in which case it may not >> be mapped meaning SIGBUS won't be delivered. > Sorry, I don't remember, what is the scenario where KVM can have a > mapping in stage 2 without there being a corresponding mapping for user > space? (looks like I mean more than one thing by mapping... oops.) Mapping in that there is a physical page for this user-space address, but when qemu first touches it, it will be faulted in as its not been touched before. (rambling on:) When mm/memory_failure.c:memory_failure() walks the rmap for the poisoned page it doesn't find qemu, so no user-space processes gets signalled. If qemu were to touch the page, fixup_user_fault() will return -EHWPOISON and we deliver sigbus to qemu. This doesn't happen when the guest touches the page as kvm's core code maps -EHWPOISON to KVM_PFN_ERR_HWPOISON, which the arm/arm64 kvm code ignores and drops -EFAULT on userspace instead. >> This works well until a guest accesses that page, and KVM discovers >> pfn == KVM_PFN_ERR_HWPOISON when it comes to process the stage2 fault. >> >> Do as x86 does, and deliver the SIGBUS when we discover >> KVM_PFN_ERR_HWPOISON. Use the stage2 mapping size as the si_addr_lsb > > But this part about the stage 2 mapping size is not what the code does. > It uses the granularity of the mmap region, if I'm not mistaken. Yes. This is what I got wrong last time, Punit put me right, but I forgot to update the commit message. I will change this 'Use the'... sentence in v3 to: > Use the hugepage size as si_addr_lsb if this vma was allocated as a hugepage. > Transparent hugepages will be split by memory_failure() before we see them > here. Thanks, James _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
