From: David Stevens <stevensd@xxxxxxxxxxxx> This patch series adds support for mapping VM_IO and VM_PFNMAP memory that is backed by struct pages that aren't currently being refcounted (e.g. tail pages of non-compound higher order allocations) into the guest. Our use case is virtio-gpu blob resources [1], which directly map host graphics buffers into the guest as "vram" for the virtio-gpu device. This feature currently does not work on systems using the amdgpu driver, as that driver allocates non-compound higher order pages via ttm_pool_alloc_page. Currently, the gfn_to_pfn functions require being able to pin the target pfn, so they fail when the pfn returned by follow_pte isn't a ref-counted page. However, the KVM secondary MMUs do not require that the pfn be pinned, since they are integrated with the mmu notifier API. This series adds a new set of gfn_to_pfn_noref functions which parallel the gfn_to_pfn functions but do not pin the pfn. The new functions return the page from gup if it was present, so callers can use it and call put_page when done. This series updates x86 and arm64 secondary MMUs to the new API. Other MMUs can likely be updated without too much difficulty, but I am not familiar with them and have no way to test them. On the other hand, updating the rest of KVM would require replacing all usages of kvm_vcpu_map with the gfn_to_pfn_cache, which is not at all easy [2]. [1] https://patchwork.kernel.org/project/dri-devel/cover/20200814024000.2485-1-gurchetansingh@xxxxxxxxxxxx/ [2] https://lore.kernel.org/all/ZBEEQtmtNPaEqU1i@xxxxxxxxxx/ v5 -> v6: - rebase on kvm next branch - rename gfn_to_pfn_page to gfn_to_pfn_noref - fix uninitialized outparam in error case of __kvm_faultin_pfn - add kvm_release_pfn_noref_clean for releasing pfn/page pair v4 -> v5: - rebase on kvm next branch again v3 -> v4: - rebase on kvm next branch again - Add some more context to a comment in ensure_pfn_ref v2 -> v3: - rebase on kvm next branch v1 -> v2: - Introduce new gfn_to_pfn_page functions instead of modifying the behavior of existing gfn_to_pfn functions, to make the change less invasive. - Drop changes to mmu_audit.c - Include Nicholas Piggin's patch to avoid corrupting refcount in the follow_pte case, and use it in depreciated gfn_to_pfn functions. - Rebase on kvm/next David Stevens (4): KVM: mmu: introduce new gfn_to_pfn_noref functions KVM: x86/mmu: use gfn_to_pfn_noref KVM: arm64/mmu: use gfn_to_pfn_noref KVM: mmu: remove over-aggressive warnings arch/arm64/kvm/mmu.c | 21 ++-- arch/x86/kvm/mmu/mmu.c | 29 ++--- arch/x86/kvm/mmu/mmu_internal.h | 1 + arch/x86/kvm/mmu/paging_tmpl.h | 7 +- arch/x86/kvm/x86.c | 5 +- include/linux/kvm_host.h | 18 +++ virt/kvm/kvm_main.c | 214 +++++++++++++++++++++++--------- virt/kvm/kvm_mm.h | 6 +- virt/kvm/pfncache.c | 12 +- 9 files changed, 220 insertions(+), 93 deletions(-) -- 2.40.0.348.gf938b09366-goog
