arm64 folks, the first two patches are bug fixes, but I have very low confidence that they are correct and/or desirable. If they are more or less correct, I can post them separately if that'd make life easier. I included them here to avoid conflicts, and because I'm pretty sure how KVM deals with MTE tags vs. dirty logging will impact what APIs KVM needs to provide to arch code.
On to the series... The TL;DR is that I would like to get input on two things: 1. Marking folios dirty/accessed only on the intial stage-2 page fault 2. The new APIs for faulting, prefetching, and doing "lookups" on pfns This is (spiritually) v12 of David Steven's series to play nice with pfns that are "valid", i.e. have a struct page, but are not refcounted. Whereas David's series only (mostly) fixed things for x86, this series goes for broke and completely eliminates KVM's long-standing (and heinous) behavior of essentially guessing which pfns are refcounted pages (see kvm_pfn_to_refcounted_page()). Getting there requires "fixing" arch code that isn't obviously broken. Specifically, to get rid of kvm_pfn_to_refcounted_page(), KVM needs to stop marking pages/folios dirty/accessed based solely on the pfn that's stored in KVM's stage-2 page tables. In v11, KVM x86 did this by tagging SPTEs with a flag (using a software-available bit). But that isn't a viable option for some flavors of x86 (we're out of software-available bits), and more importantly I've convinced myself[*] that marking folios _dirty_ after SPTEs have been installed is completely unnecessary, and that marking folios accessed is likewise unnecessary for real world workloads (and if this is a sticking point, I have ideas on how to handle it more gracefully; more at the bottom). So, instead of tracking which SPTEs correspond to refcounted pages, v12 simply removes all of the code that operates on "struct page" based on the pfn in stage-2 PTEs. This is the back ~40-50% of the series. Most of the patches are relevatively uninteresting from a code perspective, it's the concept itself (of not marking folios dirty/accessed from SPTEs) that needs discussion. For x86 in particular, which sets accessed/dirty status when that info would be "lost", e.g. when SPTEs are zapped or KVM clears the dirty flag in a SPTE, foregoing the updates provides very measurable performance improvements for related operations. E.g. when clearing dirty bits as part of dirty logging, and zapping SPTEs to reconstitue huge pages when disabling dirty logging. The other big change from v11 is that I opted to go with dedicated, specific, and hopefully descriptive APIs to wrap kvm_follow_pfn() instead of expose the "inner" helper to arch code. In part because I still don't love kvm_follow_pfn(), and fewer callers means its easier to change if/when someone comes up with a better name. But also because I think/hope that having dedicated APIs will make it easier for arch developers to understand what is the right/preferred way to do certain operations. E.g. so that all architectures use the same core flow for handling stage-2 page faults. Long term, I would love to standardize that code even more, but this series is already waaaay too big. Along the way, I also discovered that several of the inputs to hva_to_pfn() (and it's myriad wrappers) could be removed. E.g. the rather weirdly named @atomic flag can be removed by deduplicating x86's prefetching code. As for capturing accessed information on zapped SPTEs, e.g. to prevent losing accessed information because NUMA balancing mucks with things, my thought is that arch code can preserve the accessed information in SPTEs that are unmapped/zapped because protections were modified, e.g. so that LRU-initiated aging can still collect information. I'm not at all convinced that this is necessary outside of tests that care about exact counts, e.g. KVM selftests, but I'll post an RFC KVM x86 series to get the conversation started. Note, I'm purposefully not capturing the delta from v11=>v12, because there is zero chance I will get everything, and while this is a spiritual successor to David's v11, in practice it's like 98% new code. [*] https://lore.kernel.org/all/20240320005024.3216282-1-sea...@google.com David Stevens (3): KVM: Replace "async" pointer in gfn=>pfn with "no_wait" and error code KVM: Introduce kvm_follow_pfn() to eventually replace "gfn_to_pfn" APIs KVM: Migrate kvm_vcpu_map() to kvm_follow_pfn() Sean Christopherson (81): KVM: arm64: Release pfn, i.e. put page, if copying MTE tags hits ZONE_DEVICE KVM: arm64: Disallow copying MTE to guest memory while KVM is dirty logging KVM: Drop KVM_ERR_PTR_BAD_PAGE and instead return NULL to indicate an error KVM: Allow calling kvm_release_page_{clean,dirty}() on a NULL page pointer KVM: Add kvm_release_page_unused() API to put pages that KVM never consumes KVM: x86/mmu: Skip the "try unsync" path iff the old SPTE was a leaf SPTE KVM: x86/mmu: Mark folio dirty when creating SPTE, not when zapping/modifying KVM: x86/mmu: Mark page/folio accessed only when zapping leaf SPTEs KVM: x86/mmu: Don't force flush if SPTE update clears Accessed bit KVM: x86/mmu: Use gfn_to_page_many_atomic() when prefetching indirect PTEs KVM: Rename gfn_to_page_many_atomic() to kvm_prefetch_pages() KVM: Drop @atomic param from gfn=>pfn and hva=>pfn APIs KVM: Annotate that all paths in hva_to_pfn() might sleep KVM: x86/mmu: Drop kvm_page_fault.hva, i.e. don't track intermediate hva KVM: Drop unused "hva" pointer from __gfn_to_pfn_memslot() KVM: Remove pointless sanity check on @map param to kvm_vcpu_(un)map() KVM: Explicitly initialize all fields at the start of kvm_vcpu_map() KVM: Use NULL for struct page pointer to indicate mremapped memory KVM: nVMX: Rely on kvm_vcpu_unmap() to track validity of eVMCS mapping KVM: nVMX: Drop pointless msr_bitmap_map field from struct nested_vmx KVM: nVMX: Add helper to put (unmap) vmcs12 pages KVM: Use plain "struct page" pointer instead of single-entry array KVM: Provide refcounted page as output field in struct kvm_follow_pfn KVM: Move kvm_{set,release}_page_{clean,dirty}() helpers up in kvm_main.c KVM: pfncache: Precisely track refcounted pages KVM: Pin (as in FOLL_PIN) pages during kvm_vcpu_map() KVM: nVMX: Mark vmcs12's APIC access page dirty when unmapping KVM: Pass in write/dirty to kvm_vcpu_map(), not kvm_vcpu_unmap() KVM: Get writable mapping for __kvm_vcpu_map() only when necessary KVM: Disallow direct access (w/o mmu_notifier) to unpinned pfn by default KVM: Add a helper to lookup a pfn without grabbing a reference KVM: x86: Use kvm_lookup_pfn() to check if retrying #PF is useful KVM: x86: Use kvm_lookup_pfn() to check if APIC access page was installed KVM: x86/mmu: Add "mmu" prefix fault-in helpers to free up generic names KVM: x86/mmu: Put direct prefetched pages via kvm_release_page_clean() KVM: x86/mmu: Add common helper to handle prefetching SPTEs KVM: x86/mmu: Add helper to "finish" handling a guest page fault KVM: x86/mmu: Mark pages/folios dirty at the origin of make_spte() KVM: Move declarations of memslot accessors up in kvm_host.h KVM: Add kvm_faultin_pfn() to specifically service guest page faults KVM: x86/mmu: Convert page fault paths to kvm_faultin_pfn() KVM: guest_memfd: Provide "struct page" as output from kvm_gmem_get_pfn() KVM: x86/mmu: Put refcounted pages instead of blindly releasing pfns KVM: x86/mmu: Don't mark unused faultin pages as accessed KVM: Move x86's API to release a faultin page to common KVM KVM: VMX: Hold mmu_lock until page is released when updating APIC access page KVM: VMX: Use __kvm_faultin_page() to get APIC access page/pfn KVM: PPC: e500: Mark "struct page" dirty in kvmppc_e500_shadow_map() KVM: PPC: e500: Mark "struct page" pfn accessed before dropping mmu_lock KVM: PPC: e500: Use __kvm_faultin_pfn() to handle page faults KVM: arm64: Mark "struct page" pfns accessed/dirty before dropping mmu_lock KVM: arm64: Use __kvm_faultin_pfn() to handle memory aborts KVM: RISC-V: Mark "struct page" pfns dirty iff a stage-2 PTE is installed KVM: RISC-V: Mark "struct page" pfns accessed before dropping mmu_lock KVM: RISC-V: Use kvm_faultin_pfn() when mapping pfns into the guest KVM: PPC: Use __kvm_faultin_pfn() to handle page faults on Book3s HV KVM: PPC: Use __kvm_faultin_pfn() to handle page faults on Book3s Radix KVM: PPC: Drop unused @kvm_ro param from kvmppc_book3s_instantiate_page() KVM: PPC: Book3S: Mark "struct page" pfns dirty/accessed after installing PTE KVM: PPC: Use kvm_faultin_pfn() to handle page faults on Book3s PR KVM: LoongArch: Mark "struct page" pfns dirty only in "slow" page fault path KVM: LoongArch: Mark "struct page" pfns accessed only in "slow" page fault path KVM: LoongArch: Mark "struct page" pfn accessed before dropping mmu_lock KVM: LoongArch: Use kvm_faultin_pfn() to map pfns into the guest KVM: MIPS: Mark "struct page" pfns dirty only in "slow" page fault path KVM: MIPS: Mark "struct page" pfns accessed only in "slow" page fault path KVM: MIPS: Mark "struct page" pfns accessed prior to dropping mmu_lock KVM: MIPS: Use kvm_faultin_pfn() to map pfns into the guest KVM: PPC: Remove extra get_page() to fix page refcount leak KVM: PPC: Use kvm_vcpu_map() to map guest memory to patch dcbz instructions KVM: Convert gfn_to_page() to use kvm_follow_pfn() KVM: Add support for read-only usage of gfn_to_page() KVM: arm64: Use __gfn_to_page() when copying MTE tags to/from userspace KVM: PPC: Explicitly require struct page memory for Ultravisor sharing KVM: Drop gfn_to_pfn() APIs now that all users are gone KVM: s390: Use kvm_release_page_dirty() to unpin "struct page" memory KVM: Make kvm_follow_pfn.refcounted_page a required field KVM: x86/mmu: Don't mark "struct page" accessed when zapping SPTEs KVM: arm64: Don't mark "struct page" accessed when making SPTE young KVM: Drop APIs that manipulate "struct page" via pfns KVM: Don't grab reference on VM_MIXEDMAP pfns that have a "struct page" Documentation/virt/kvm/locking.rst | 80 ++-- arch/arm64/include/asm/kvm_pgtable.h | 4 +- arch/arm64/kvm/guest.c | 25 +- arch/arm64/kvm/hyp/pgtable.c | 7 +- arch/arm64/kvm/mmu.c | 21 +- arch/loongarch/kvm/mmu.c | 40 +- arch/mips/kvm/mmu.c | 26 +- arch/powerpc/include/asm/kvm_book3s.h | 4 +- arch/powerpc/kvm/book3s.c | 7 +- arch/powerpc/kvm/book3s_32_mmu_host.c | 7 +- arch/powerpc/kvm/book3s_64_mmu_host.c | 12 +- arch/powerpc/kvm/book3s_64_mmu_hv.c | 25 +- arch/powerpc/kvm/book3s_64_mmu_radix.c | 35 +- arch/powerpc/kvm/book3s_hv_nested.c | 4 +- arch/powerpc/kvm/book3s_hv_uvmem.c | 25 +- arch/powerpc/kvm/book3s_pr.c | 14 +- arch/powerpc/kvm/book3s_xive_native.c | 2 +- arch/powerpc/kvm/e500_mmu_host.c | 19 +- arch/riscv/kvm/mmu.c | 9 +- arch/s390/kvm/vsie.c | 4 +- arch/x86/kvm/lapic.c | 15 +- arch/x86/kvm/mmu/mmu.c | 191 ++++---- arch/x86/kvm/mmu/mmu_internal.h | 5 +- arch/x86/kvm/mmu/paging_tmpl.h | 29 +- arch/x86/kvm/mmu/spte.c | 23 +- arch/x86/kvm/mmu/tdp_mmu.c | 16 - arch/x86/kvm/svm/nested.c | 4 +- arch/x86/kvm/svm/sev.c | 12 +- arch/x86/kvm/svm/svm.c | 8 +- arch/x86/kvm/vmx/nested.c | 42 +- arch/x86/kvm/vmx/vmx.c | 28 +- arch/x86/kvm/vmx/vmx.h | 2 - arch/x86/kvm/x86.c | 16 +- include/linux/kvm_host.h | 124 +++-- virt/kvm/guest_memfd.c | 19 +- virt/kvm/kvm_main.c | 603 ++++++++++--------------- virt/kvm/kvm_mm.h | 36 +- virt/kvm/pfncache.c | 20 +- 38 files changed, 698 insertions(+), 865 deletions(-) base-commit: 332d2c1d713e232e163386c35a3ba0c1b90df83f -- 2.46.0.rc1.232.g9752f9e123-goog
