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    SubjectRe: [PATCH 13/22] kvm: mmu: Support invalidate range MMU notifier for TDP MMU
    On Fri, Sep 25, 2020 at 02:22:53PM -0700, Ben Gardon wrote:
    > In order to interoperate correctly with the rest of KVM and other Linux
    > subsystems, the TDP MMU must correctly handle various MMU notifiers. Add
    > hooks to handle the invalidate range family of MMU notifiers.
    >
    > Tested by running kvm-unit-tests and KVM selftests on an Intel Haswell
    > machine. This series introduced no new failures.
    >
    > This series can be viewed in Gerrit at:
    > https://linux-review.googlesource.com/c/virt/kvm/kvm/+/2538
    >
    > Signed-off-by: Ben Gardon <bgardon@google.com>
    > ---
    > arch/x86/kvm/mmu/mmu.c | 9 ++++-
    > arch/x86/kvm/mmu/tdp_mmu.c | 80 +++++++++++++++++++++++++++++++++++---
    > arch/x86/kvm/mmu/tdp_mmu.h | 3 ++
    > 3 files changed, 86 insertions(+), 6 deletions(-)
    >
    > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
    > index 52d661a758585..0ddfdab942554 100644
    > --- a/arch/x86/kvm/mmu/mmu.c
    > +++ b/arch/x86/kvm/mmu/mmu.c
    > @@ -1884,7 +1884,14 @@ static int kvm_handle_hva(struct kvm *kvm, unsigned long hva,
    > int kvm_unmap_hva_range(struct kvm *kvm, unsigned long start, unsigned long end,
    > unsigned flags)
    > {
    > - return kvm_handle_hva_range(kvm, start, end, 0, kvm_unmap_rmapp);
    > + int r;
    > +
    > + r = kvm_handle_hva_range(kvm, start, end, 0, kvm_unmap_rmapp);
    > +
    > + if (kvm->arch.tdp_mmu_enabled)
    > + r |= kvm_tdp_mmu_zap_hva_range(kvm, start, end);

    Similar to an earlier question, is this intentionally additive, or can this
    instead by:

    if (kvm->arch.tdp_mmu_enabled)
    r = kvm_tdp_mmu_zap_hva_range(kvm, start, end);
    else
    r = kvm_handle_hva_range(kvm, start, end, 0, kvm_unmap_rmapp);

    > +
    > + return r;
    > }
    >
    > int kvm_set_spte_hva(struct kvm *kvm, unsigned long hva, pte_t pte)
    > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
    > index 557e780bdf9f9..1cea58db78a13 100644
    > --- a/arch/x86/kvm/mmu/tdp_mmu.c
    > +++ b/arch/x86/kvm/mmu/tdp_mmu.c
    > @@ -60,7 +60,7 @@ bool is_tdp_mmu_root(struct kvm *kvm, hpa_t hpa)
    > }
    >
    > static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
    > - gfn_t start, gfn_t end);
    > + gfn_t start, gfn_t end, bool can_yield);
    >
    > static void free_tdp_mmu_root(struct kvm *kvm, struct kvm_mmu_page *root)
    > {
    > @@ -73,7 +73,7 @@ static void free_tdp_mmu_root(struct kvm *kvm, struct kvm_mmu_page *root)
    >
    > list_del(&root->link);
    >
    > - zap_gfn_range(kvm, root, 0, max_gfn);
    > + zap_gfn_range(kvm, root, 0, max_gfn, false);
    >
    > free_page((unsigned long)root->spt);
    > kmem_cache_free(mmu_page_header_cache, root);
    > @@ -361,9 +361,14 @@ static bool tdp_mmu_iter_cond_resched(struct kvm *kvm, struct tdp_iter *iter)
    > * non-root pages mapping GFNs strictly within that range. Returns true if
    > * SPTEs have been cleared and a TLB flush is needed before releasing the
    > * MMU lock.
    > + * If can_yield is true, will release the MMU lock and reschedule if the
    > + * scheduler needs the CPU or there is contention on the MMU lock. If this
    > + * function cannot yield, it will not release the MMU lock or reschedule and
    > + * the caller must ensure it does not supply too large a GFN range, or the
    > + * operation can cause a soft lockup.
    > */
    > static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
    > - gfn_t start, gfn_t end)
    > + gfn_t start, gfn_t end, bool can_yield)
    > {
    > struct tdp_iter iter;
    > bool flush_needed = false;
    > @@ -387,7 +392,10 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
    > handle_changed_spte(kvm, as_id, iter.gfn, iter.old_spte, 0,
    > iter.level);
    >
    > - flush_needed = !tdp_mmu_iter_cond_resched(kvm, &iter);
    > + if (can_yield)
    > + flush_needed = !tdp_mmu_iter_cond_resched(kvm, &iter);

    flush_needed = !can_yield || !tdp_mmu_iter_cond_resched(kvm, &iter);

    > + else
    > + flush_needed = true;
    > }
    > return flush_needed;
    > }
    > @@ -410,7 +418,7 @@ bool kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, gfn_t start, gfn_t end)
    > */
    > get_tdp_mmu_root(kvm, root);
    >
    > - flush = zap_gfn_range(kvm, root, start, end) || flush;
    > + flush = zap_gfn_range(kvm, root, start, end, true) || flush;
    >
    > put_tdp_mmu_root(kvm, root);
    > }
    > @@ -551,3 +559,65 @@ int kvm_tdp_mmu_page_fault(struct kvm_vcpu *vcpu, int write, int map_writable,
    >
    > return ret;
    > }
    > +
    > +static int kvm_tdp_mmu_handle_hva_range(struct kvm *kvm, unsigned long start,
    > + unsigned long end, unsigned long data,
    > + int (*handler)(struct kvm *kvm, struct kvm_memory_slot *slot,
    > + struct kvm_mmu_page *root, gfn_t start,
    > + gfn_t end, unsigned long data))
    > +{
    > + struct kvm_memslots *slots;
    > + struct kvm_memory_slot *memslot;
    > + struct kvm_mmu_page *root;
    > + int ret = 0;
    > + int as_id;
    > +
    > + for_each_tdp_mmu_root(kvm, root) {
    > + /*
    > + * Take a reference on the root so that it cannot be freed if
    > + * this thread releases the MMU lock and yields in this loop.
    > + */
    > + get_tdp_mmu_root(kvm, root);
    > +
    > + as_id = kvm_mmu_page_as_id(root);
    > + slots = __kvm_memslots(kvm, as_id);
    > + kvm_for_each_memslot(memslot, slots) {
    > + unsigned long hva_start, hva_end;
    > + gfn_t gfn_start, gfn_end;
    > +
    > + hva_start = max(start, memslot->userspace_addr);
    > + hva_end = min(end, memslot->userspace_addr +
    > + (memslot->npages << PAGE_SHIFT));
    > + if (hva_start >= hva_end)
    > + continue;
    > + /*
    > + * {gfn(page) | page intersects with [hva_start, hva_end)} =
    > + * {gfn_start, gfn_start+1, ..., gfn_end-1}.
    > + */
    > + gfn_start = hva_to_gfn_memslot(hva_start, memslot);
    > + gfn_end = hva_to_gfn_memslot(hva_end + PAGE_SIZE - 1, memslot);
    > +
    > + ret |= handler(kvm, memslot, root, gfn_start,
    > + gfn_end, data);

    Eh, I'd say let this one poke out, the above hva_to_gfn_memslot() already
    overruns 80 chars. IMO it's more readable without the wraps.

    > + }
    > +
    > + put_tdp_mmu_root(kvm, root);
    > + }
    > +
    > + return ret;
    > +}
    > +
    > +static int zap_gfn_range_hva_wrapper(struct kvm *kvm,
    > + struct kvm_memory_slot *slot,
    > + struct kvm_mmu_page *root, gfn_t start,
    > + gfn_t end, unsigned long unused)
    > +{
    > + return zap_gfn_range(kvm, root, start, end, false);
    > +}
    > +
    > +int kvm_tdp_mmu_zap_hva_range(struct kvm *kvm, unsigned long start,
    > + unsigned long end)
    > +{
    > + return kvm_tdp_mmu_handle_hva_range(kvm, start, end, 0,
    > + zap_gfn_range_hva_wrapper);
    > +}
    > diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
    > index abf23dc0ab7ad..ce804a97bfa1d 100644
    > --- a/arch/x86/kvm/mmu/tdp_mmu.h
    > +++ b/arch/x86/kvm/mmu/tdp_mmu.h
    > @@ -18,4 +18,7 @@ void kvm_tdp_mmu_zap_all(struct kvm *kvm);
    > int kvm_tdp_mmu_page_fault(struct kvm_vcpu *vcpu, int write, int map_writable,
    > int level, gpa_t gpa, kvm_pfn_t pfn, bool prefault,
    > bool lpage_disallowed);
    > +
    > +int kvm_tdp_mmu_zap_hva_range(struct kvm *kvm, unsigned long start,
    > + unsigned long end);
    > #endif /* __KVM_X86_MMU_TDP_MMU_H */
    > --
    > 2.28.0.709.gb0816b6eb0-goog
    >

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