Hi Gavin, On 2021/4/21 14:20, Gavin Shan wrote: > Hi Keqian and Santosh, > > On 4/21/21 12:59 PM, Keqian Zhu wrote: >> On 2020/10/22 0:16, Santosh Shukla wrote: >>> The Commit:6d674e28 introduces a notion to detect and handle the >>> device mapping. The commit checks for the VM_PFNMAP flag is set >>> in vma->flags and if set then marks force_pte to true such that >>> if force_pte is true then ignore the THP function check >>> (/transparent_hugepage_adjust()). >>> >>> There could be an issue with the VM_PFNMAP flag setting and checking. >>> For example consider a case where the mdev vendor driver register's >>> the vma_fault handler named vma_mmio_fault(), which maps the >>> host MMIO region in-turn calls remap_pfn_range() and maps >>> the MMIO's vma space. Where, remap_pfn_range implicitly sets >>> the VM_PFNMAP flag into vma->flags. >> Could you give the name of the mdev vendor driver that triggers this issue? >> I failed to find one according to your description. Thanks. >> > > I think it would be fixed in driver side to set VM_PFNMAP in > its mmap() callback (call_mmap()), like vfio PCI driver does. > It means it won't be delayed until page fault is issued and > remap_pfn_range() is called. It's determined from the beginning > that the vma associated the mdev vendor driver is serving as > PFN remapping purpose. So the vma should be populated completely, > including the VM_PFNMAP flag before it becomes visible to user > space. > > The example can be found from vfio driver in drivers/vfio/pci/vfio_pci.c: > vfio_pci_mmap: VM_PFNMAP is set for the vma > vfio_pci_mmap_fault: remap_pfn_range() is called Right. I have discussed the above with Marc. I want to find the driver to fix it. However, AFAICS, there is no driver matches the description... Thanks, Keqian > > Thanks, > Gavin > >>> >>> Now lets assume a mmio fault handing flow where guest first access >>> the MMIO region whose 2nd stage translation is not present. >>> So that results to arm64-kvm hypervisor executing guest abort handler, >>> like below: >>> >>> kvm_handle_guest_abort() --> >>> user_mem_abort()--> { >>> >>> ... >>> 0. checks the vma->flags for the VM_PFNMAP. >>> 1. Since VM_PFNMAP flag is not yet set so force_pte _is_ false; >>> 2. gfn_to_pfn_prot() --> >>> __gfn_to_pfn_memslot() --> >>> fixup_user_fault() --> >>> handle_mm_fault()--> >>> __do_fault() --> >>> vma_mmio_fault() --> // vendor's mdev fault handler >>> remap_pfn_range()--> // Here sets the VM_PFNMAP >>> flag into vma->flags. >>> 3. Now that force_pte is set to false in step-2), >>> will execute transparent_hugepage_adjust() func and >>> that lead to Oops [4]. >>> } >>> >>> The proposition is to check is_iomap flag before executing the THP >>> function transparent_hugepage_adjust(). >>> >>> [4] THP Oops: >>>> pc: kvm_is_transparent_hugepage+0x18/0xb0 >>>> ... >>>> ... >>>> user_mem_abort+0x340/0x9b8 >>>> kvm_handle_guest_abort+0x248/0x468 >>>> handle_exit+0x150/0x1b0 >>>> kvm_arch_vcpu_ioctl_run+0x4d4/0x778 >>>> kvm_vcpu_ioctl+0x3c0/0x858 >>>> ksys_ioctl+0x84/0xb8 >>>> __arm64_sys_ioctl+0x28/0x38 >>> >>> Tested on Huawei Kunpeng Taishan-200 arm64 server, Using VFIO-mdev device. >>> Linux tip: 583090b1 >>> >>> Fixes: 6d674e28 ("KVM: arm/arm64: Properly handle faulting of device mappings") >>> Signed-off-by: Santosh Shukla <sashukla@xxxxxxxxxx> >>> --- >>> arch/arm64/kvm/mmu.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c >>> index 3d26b47..ff15357 100644 >>> --- a/arch/arm64/kvm/mmu.c >>> +++ b/arch/arm64/kvm/mmu.c >>> @@ -1947,7 +1947,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, >>> * If we are not forced to use page mapping, check if we are >>> * backed by a THP and thus use block mapping if possible. >>> */ >>> - if (vma_pagesize == PAGE_SIZE && !force_pte) >>> + if (vma_pagesize == PAGE_SIZE && !force_pte && !is_iomap(flags)) >>> vma_pagesize = transparent_hugepage_adjust(memslot, hva, >>> &pfn, &fault_ipa); >>> if (writable) >>> >> > > . > _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm