Re: [PATCH] KVM: arm64: Skip CMOs when updating a PTE pointing to non-memory
From: Alexandru Elisei <hidden>
Date: 2021-04-27 14:54:03
Also in:
kvm, kvmarm
Subsystem:
the rest · Maintainer:
Linus Torvalds
Hi, I've been trying to reproduce the panic, but I haven't had any success. With a known working PCI passtrough device, this is how I changed kvmtool:
diff --git a/vfio/core.c b/vfio/core.c
index 3ff2c0b..b4ee7e9 100644
--- a/vfio/core.c
+++ b/vfio/core.c@@ -261,6 +261,9 @@ int vfio_map_region(struct kvm *kvm, struct vfio_device *vdev,return ret; } + char c = *(char *)base; + fprintf(stderr, "c = %c\n", c); + return 0; } What the change is doing is reading from the BAR region after it's has been mmap'ed into userspace. I can see that the read hits vfio_pci_mmap_fault(), which calls io_remap_pfn_range(), but I can't figure out how I can trigger the MMU notifiers. Any suggestions? The comment [1] suggested that the panic is triggered during page aging. vfio_pci_mmap() sets the VM_PFNMAP for the VMA and I see in the Documentation that pages with VM_PFNMAP are added to the unevictable LRU list, doesn't that mean it's not subject the page aging? I feel like there's something I'm missing. [1] https://lore.kernel.org/kvm/BY5PR12MB37642B9AC7E5D907F5A664F6B3459@BY5PR12MB3764.namprd12.prod.outlook.com/ (local) Thanks, Alex On 4/26/21 11:36 AM, Marc Zyngier wrote:
quoted hunk ↗ jump to hunk
Sumit Gupta and Krishna Reddy both reported that for MMIO regions mapped into userspace using VFIO, a PTE update can trigger a MMU notifier reaching kvm_set_spte_hva(). There is an assumption baked in kvm_set_spte_hva() that it only deals with memory pages, and not MMIO. For this purpose, it performs a cache cleaning of the potentially newly mapped page. However, for a MMIO range, this explodes as there is no linear mapping for this range (and doing cache maintenance on it would make little sense anyway). Check for the validity of the page before performing the CMO addresses the problem. Reported-by: Krishna Reddy <vdumpa@nvidia.com> Reported-by: Sumit Gupta <sumitg@nvidia.com>, Tested-by: Sumit Gupta <sumitg@nvidia.com>, Signed-off-by: Marc Zyngier <maz@kernel.org> Link: https://lore.kernel.org/r/5a8825bc-286e-b316-515f-3bd3c9c70a80@nvidia.com (local) --- arch/arm64/kvm/mmu.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index cd4d51ae3d4a..564a0f7fcd05 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c@@ -1236,7 +1236,8 @@ int kvm_set_spte_hva(struct kvm *kvm, unsigned long hva, pte_t pte) * We've moved a page around, probably through CoW, so let's treat it * just like a translation fault and clean the cache to the PoC. */ - clean_dcache_guest_page(pfn, PAGE_SIZE); + if (!kvm_is_device_pfn(pfn)) + clean_dcache_guest_page(pfn, PAGE_SIZE); handle_hva_to_gpa(kvm, hva, end, &kvm_set_spte_handler, &pfn); return 0; }
_______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel