| Message ID | 20231027182217.3615211-11-seanjc@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | KVM: guest_memfd() and per-page attributes | expand |
On 10/27/23 20:21, Sean Christopherson wrote: > Handle AMD SEV's kvm_arch_guest_memory_reclaimed() hook by having > __kvm_handle_hva_range() return whether or not an overlapping memslot > was found, i.e. mmu_lock was acquired. Using the .on_unlock() hook > works, but kvm_arch_guest_memory_reclaimed() needs to run after dropping > mmu_lock, which makes .on_lock() and .on_unlock() asymmetrical. > > Use a small struct to return the tuple of the notifier-specific return, > plus whether or not overlap was found. Because the iteration helpers are > __always_inlined, practically speaking, the struct will never actually be > returned from a function call (not to mention the size of the struct will > be two bytes in practice). Could have been split in two patches, but it's fine anyway. Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> Paolo
On Fri, Oct 27, 2023 at 7:22 PM Sean Christopherson <seanjc@google.com> wrote: > > Handle AMD SEV's kvm_arch_guest_memory_reclaimed() hook by having > __kvm_handle_hva_range() return whether or not an overlapping memslot > was found, i.e. mmu_lock was acquired. Using the .on_unlock() hook > works, but kvm_arch_guest_memory_reclaimed() needs to run after dropping > mmu_lock, which makes .on_lock() and .on_unlock() asymmetrical. > > Use a small struct to return the tuple of the notifier-specific return, > plus whether or not overlap was found. Because the iteration helpers are > __always_inlined, practically speaking, the struct will never actually be > returned from a function call (not to mention the size of the struct will > be two bytes in practice). > > Signed-off-by: Sean Christopherson <seanjc@google.com> > --- Reviewed-by: Fuad Tabba <tabba@google.com> Tested-by: Fuad Tabba <tabba@google.com> Cheers, /fuad > virt/kvm/kvm_main.c | 53 +++++++++++++++++++++++++++++++-------------- > 1 file changed, 37 insertions(+), 16 deletions(-) > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 3f5b7c2c5327..2bc04c8ae1f4 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -561,6 +561,19 @@ struct kvm_mmu_notifier_range { > bool may_block; > }; > > +/* > + * The inner-most helper returns a tuple containing the return value from the > + * arch- and action-specific handler, plus a flag indicating whether or not at > + * least one memslot was found, i.e. if the handler found guest memory. > + * > + * Note, most notifiers are averse to booleans, so even though KVM tracks the > + * return from arch code as a bool, outer helpers will cast it to an int. :-( > + */ > +typedef struct kvm_mmu_notifier_return { > + bool ret; > + bool found_memslot; > +} kvm_mn_ret_t; > + > /* > * Use a dedicated stub instead of NULL to indicate that there is no callback > * function/handler. The compiler technically can't guarantee that a real > @@ -582,22 +595,25 @@ static const union kvm_mmu_notifier_arg KVM_MMU_NOTIFIER_NO_ARG; > node; \ > node = interval_tree_iter_next(node, start, last)) \ > > -static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, > - const struct kvm_mmu_notifier_range *range) > +static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm, > + const struct kvm_mmu_notifier_range *range) > { > - bool ret = false, locked = false; > + struct kvm_mmu_notifier_return r = { > + .ret = false, > + .found_memslot = false, > + }; > struct kvm_gfn_range gfn_range; > struct kvm_memory_slot *slot; > struct kvm_memslots *slots; > int i, idx; > > if (WARN_ON_ONCE(range->end <= range->start)) > - return 0; > + return r; > > /* A null handler is allowed if and only if on_lock() is provided. */ > if (WARN_ON_ONCE(IS_KVM_NULL_FN(range->on_lock) && > IS_KVM_NULL_FN(range->handler))) > - return 0; > + return r; > > idx = srcu_read_lock(&kvm->srcu); > > @@ -631,8 +647,8 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, > gfn_range.end = hva_to_gfn_memslot(hva_end + PAGE_SIZE - 1, slot); > gfn_range.slot = slot; > > - if (!locked) { > - locked = true; > + if (!r.found_memslot) { > + r.found_memslot = true; > KVM_MMU_LOCK(kvm); > if (!IS_KVM_NULL_FN(range->on_lock)) > range->on_lock(kvm); > @@ -640,14 +656,14 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, > if (IS_KVM_NULL_FN(range->handler)) > break; > } > - ret |= range->handler(kvm, &gfn_range); > + r.ret |= range->handler(kvm, &gfn_range); > } > } > > - if (range->flush_on_ret && ret) > + if (range->flush_on_ret && r.ret) > kvm_flush_remote_tlbs(kvm); > > - if (locked) { > + if (r.found_memslot) { > KVM_MMU_UNLOCK(kvm); > if (!IS_KVM_NULL_FN(range->on_unlock)) > range->on_unlock(kvm); > @@ -655,8 +671,7 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, > > srcu_read_unlock(&kvm->srcu, idx); > > - /* The notifiers are averse to booleans. :-( */ > - return (int)ret; > + return r; > } > > static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn, > @@ -677,7 +692,7 @@ static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn, > .may_block = false, > }; > > - return __kvm_handle_hva_range(kvm, &range); > + return __kvm_handle_hva_range(kvm, &range).ret; > } > > static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn, > @@ -696,7 +711,7 @@ static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn > .may_block = false, > }; > > - return __kvm_handle_hva_range(kvm, &range); > + return __kvm_handle_hva_range(kvm, &range).ret; > } > > static bool kvm_change_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range) > @@ -798,7 +813,7 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, > .end = range->end, > .handler = kvm_mmu_unmap_gfn_range, > .on_lock = kvm_mmu_invalidate_begin, > - .on_unlock = kvm_arch_guest_memory_reclaimed, > + .on_unlock = (void *)kvm_null_fn, > .flush_on_ret = true, > .may_block = mmu_notifier_range_blockable(range), > }; > @@ -830,7 +845,13 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, > gfn_to_pfn_cache_invalidate_start(kvm, range->start, range->end, > hva_range.may_block); > > - __kvm_handle_hva_range(kvm, &hva_range); > + /* > + * If one or more memslots were found and thus zapped, notify arch code > + * that guest memory has been reclaimed. This needs to be done *after* > + * dropping mmu_lock, as x86's reclaim path is slooooow. > + */ > + if (__kvm_handle_hva_range(kvm, &hva_range).found_memslot) > + kvm_arch_guest_memory_reclaimed(kvm); > > return 0; > } > -- > 2.42.0.820.g83a721a137-goog >
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 3f5b7c2c5327..2bc04c8ae1f4 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -561,6 +561,19 @@ struct kvm_mmu_notifier_range { bool may_block; }; +/* + * The inner-most helper returns a tuple containing the return value from the + * arch- and action-specific handler, plus a flag indicating whether or not at + * least one memslot was found, i.e. if the handler found guest memory. + * + * Note, most notifiers are averse to booleans, so even though KVM tracks the + * return from arch code as a bool, outer helpers will cast it to an int. :-( + */ +typedef struct kvm_mmu_notifier_return { + bool ret; + bool found_memslot; +} kvm_mn_ret_t; + /* * Use a dedicated stub instead of NULL to indicate that there is no callback * function/handler. The compiler technically can't guarantee that a real @@ -582,22 +595,25 @@ static const union kvm_mmu_notifier_arg KVM_MMU_NOTIFIER_NO_ARG; node; \ node = interval_tree_iter_next(node, start, last)) \ -static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, - const struct kvm_mmu_notifier_range *range) +static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm, + const struct kvm_mmu_notifier_range *range) { - bool ret = false, locked = false; + struct kvm_mmu_notifier_return r = { + .ret = false, + .found_memslot = false, + }; struct kvm_gfn_range gfn_range; struct kvm_memory_slot *slot; struct kvm_memslots *slots; int i, idx; if (WARN_ON_ONCE(range->end <= range->start)) - return 0; + return r; /* A null handler is allowed if and only if on_lock() is provided. */ if (WARN_ON_ONCE(IS_KVM_NULL_FN(range->on_lock) && IS_KVM_NULL_FN(range->handler))) - return 0; + return r; idx = srcu_read_lock(&kvm->srcu); @@ -631,8 +647,8 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, gfn_range.end = hva_to_gfn_memslot(hva_end + PAGE_SIZE - 1, slot); gfn_range.slot = slot; - if (!locked) { - locked = true; + if (!r.found_memslot) { + r.found_memslot = true; KVM_MMU_LOCK(kvm); if (!IS_KVM_NULL_FN(range->on_lock)) range->on_lock(kvm); @@ -640,14 +656,14 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, if (IS_KVM_NULL_FN(range->handler)) break; } - ret |= range->handler(kvm, &gfn_range); + r.ret |= range->handler(kvm, &gfn_range); } } - if (range->flush_on_ret && ret) + if (range->flush_on_ret && r.ret) kvm_flush_remote_tlbs(kvm); - if (locked) { + if (r.found_memslot) { KVM_MMU_UNLOCK(kvm); if (!IS_KVM_NULL_FN(range->on_unlock)) range->on_unlock(kvm); @@ -655,8 +671,7 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, srcu_read_unlock(&kvm->srcu, idx); - /* The notifiers are averse to booleans. :-( */ - return (int)ret; + return r; } static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn, @@ -677,7 +692,7 @@ static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn, .may_block = false, }; - return __kvm_handle_hva_range(kvm, &range); + return __kvm_handle_hva_range(kvm, &range).ret; } static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn, @@ -696,7 +711,7 @@ static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn .may_block = false, }; - return __kvm_handle_hva_range(kvm, &range); + return __kvm_handle_hva_range(kvm, &range).ret; } static bool kvm_change_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range) @@ -798,7 +813,7 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, .end = range->end, .handler = kvm_mmu_unmap_gfn_range, .on_lock = kvm_mmu_invalidate_begin, - .on_unlock = kvm_arch_guest_memory_reclaimed, + .on_unlock = (void *)kvm_null_fn, .flush_on_ret = true, .may_block = mmu_notifier_range_blockable(range), }; @@ -830,7 +845,13 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, gfn_to_pfn_cache_invalidate_start(kvm, range->start, range->end, hva_range.may_block); - __kvm_handle_hva_range(kvm, &hva_range); + /* + * If one or more memslots were found and thus zapped, notify arch code + * that guest memory has been reclaimed. This needs to be done *after* + * dropping mmu_lock, as x86's reclaim path is slooooow. + */ + if (__kvm_handle_hva_range(kvm, &hva_range).found_memslot) + kvm_arch_guest_memory_reclaimed(kvm); return 0; }
Handle AMD SEV's kvm_arch_guest_memory_reclaimed() hook by having __kvm_handle_hva_range() return whether or not an overlapping memslot was found, i.e. mmu_lock was acquired. Using the .on_unlock() hook works, but kvm_arch_guest_memory_reclaimed() needs to run after dropping mmu_lock, which makes .on_lock() and .on_unlock() asymmetrical. Use a small struct to return the tuple of the notifier-specific return, plus whether or not overlap was found. Because the iteration helpers are __always_inlined, practically speaking, the struct will never actually be returned from a function call (not to mention the size of the struct will be two bytes in practice). Signed-off-by: Sean Christopherson <seanjc@google.com> --- virt/kvm/kvm_main.c | 53 +++++++++++++++++++++++++++++++-------------- 1 file changed, 37 insertions(+), 16 deletions(-)