[PATCH v12 00/84] KVM: Stop grabbing references to PFNMAP'd pages
Sean Christopherson
seanjc at google.com
Fri Jul 26 16:51:09 PDT 2024
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-seanjc@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
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