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Date: Wed, 18 Aug 2021 16:29:10 +0200
From: Claudio Imbrenda <imbrenda@...ux.ibm.com>
To: "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Sean Christopherson <seanjc@...gle.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Igor Mammedov <imammedo@...hat.com>,
Marc Zyngier <maz@...nel.org>,
James Morse <james.morse@....com>,
Julien Thierry <julien.thierry.kdev@...il.com>,
Suzuki K Poulose <suzuki.poulose@....com>,
Huacai Chen <chenhuacai@...nel.org>,
Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
Paul Mackerras <paulus@...abs.org>,
Christian Borntraeger <borntraeger@...ibm.com>,
Janosch Frank <frankja@...ux.ibm.com>,
David Hildenbrand <david@...hat.com>,
Cornelia Huck <cohuck@...hat.com>,
Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 05/13] KVM: Integrate gfn_to_memslot_approx() into
search_memslots()
On Fri, 13 Aug 2021 21:33:18 +0200
"Maciej S. Szmigiero" <mail@...iej.szmigiero.name> wrote:
> From: "Maciej S. Szmigiero" <maciej.szmigiero@...cle.com>
>
> s390 arch has gfn_to_memslot_approx() which is almost identical to
> search_memslots(), differing only in that in case the gfn falls in a hole
> one of the memslots bordering the hole is returned.
>
> Add this lookup mode as an option to search_memslots() so we don't have two
> almost identical functions for looking up a memslot by its gfn.
>
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@...cle.com>
Reviewed-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> ---
> arch/s390/kvm/kvm-s390.c | 39 ++-------------------------------------
> include/linux/kvm_host.h | 25 ++++++++++++++++++++++---
> virt/kvm/kvm_main.c | 2 +-
> 3 files changed, 25 insertions(+), 41 deletions(-)
>
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 4bed65dbad5e..6b3f05086fae 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -1941,41 +1941,6 @@ static long kvm_s390_set_skeys(struct kvm *kvm, struct kvm_s390_skeys *args)
> /* for consistency */
> #define KVM_S390_CMMA_SIZE_MAX ((u32)KVM_S390_SKEYS_MAX)
>
> -/*
> - * Similar to gfn_to_memslot, but returns the index of a memslot also when the
> - * address falls in a hole. In that case the index of one of the memslots
> - * bordering the hole is returned.
> - */
> -static int gfn_to_memslot_approx(struct kvm_memslots *slots, gfn_t gfn)
> -{
> - int start = 0, end = slots->used_slots;
> - int slot = atomic_read(&slots->last_used_slot);
> - struct kvm_memory_slot *memslots = slots->memslots;
> -
> - if (gfn >= memslots[slot].base_gfn &&
> - gfn < memslots[slot].base_gfn + memslots[slot].npages)
> - return slot;
> -
> - while (start < end) {
> - slot = start + (end - start) / 2;
> -
> - if (gfn >= memslots[slot].base_gfn)
> - end = slot;
> - else
> - start = slot + 1;
> - }
> -
> - if (start >= slots->used_slots)
> - return slots->used_slots - 1;
> -
> - if (gfn >= memslots[start].base_gfn &&
> - gfn < memslots[start].base_gfn + memslots[start].npages) {
> - atomic_set(&slots->last_used_slot, start);
> - }
> -
> - return start;
> -}
> -
> static int kvm_s390_peek_cmma(struct kvm *kvm, struct kvm_s390_cmma_log *args,
> u8 *res, unsigned long bufsize)
> {
> @@ -2002,8 +1967,8 @@ static int kvm_s390_peek_cmma(struct kvm *kvm, struct kvm_s390_cmma_log *args,
> static unsigned long kvm_s390_next_dirty_cmma(struct kvm_memslots *slots,
> unsigned long cur_gfn)
> {
> - int slotidx = gfn_to_memslot_approx(slots, cur_gfn);
> - struct kvm_memory_slot *ms = slots->memslots + slotidx;
> + struct kvm_memory_slot *ms = __gfn_to_memslot_approx(slots, cur_gfn, true);
> + int slotidx = ms - slots->memslots;
> unsigned long ofs = cur_gfn - ms->base_gfn;
>
> if (ms->base_gfn + ms->npages <= cur_gfn) {
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 2d62581b400e..6d0bbd6c8554 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1232,10 +1232,14 @@ try_get_memslot(struct kvm_memslots *slots, int slot_index, gfn_t gfn)
> * Returns a pointer to the memslot that contains gfn and records the index of
> * the slot in index. Otherwise returns NULL.
> *
> + * With "approx" set returns the memslot also when the address falls
> + * in a hole. In that case one of the memslots bordering the hole is
> + * returned.
> + *
> * IMPORTANT: Slots are sorted from highest GFN to lowest GFN!
> */
> static inline struct kvm_memory_slot *
> -search_memslots(struct kvm_memslots *slots, gfn_t gfn, int *index)
> +search_memslots(struct kvm_memslots *slots, gfn_t gfn, int *index, bool approx)
> {
> int start = 0, end = slots->used_slots;
> struct kvm_memory_slot *memslots = slots->memslots;
> @@ -1253,11 +1257,20 @@ search_memslots(struct kvm_memslots *slots, gfn_t gfn, int *index)
> start = slot + 1;
> }
>
> + if (approx && start >= slots->used_slots) {
> + *index = slots->used_slots - 1;
> + return &memslots[slots->used_slots - 1];
> + }
> +
> slot = try_get_memslot(slots, start, gfn);
> if (slot) {
> *index = start;
> return slot;
> }
> + if (approx) {
> + *index = start;
> + return &memslots[start];
> + }
>
> return NULL;
> }
> @@ -1268,7 +1281,7 @@ search_memslots(struct kvm_memslots *slots, gfn_t gfn, int *index)
> * itself isn't here as an inline because that would bloat other code too much.
> */
> static inline struct kvm_memory_slot *
> -__gfn_to_memslot(struct kvm_memslots *slots, gfn_t gfn)
> +__gfn_to_memslot_approx(struct kvm_memslots *slots, gfn_t gfn, bool approx)
> {
> struct kvm_memory_slot *slot;
> int slot_index = atomic_read(&slots->last_used_slot);
> @@ -1277,7 +1290,7 @@ __gfn_to_memslot(struct kvm_memslots *slots, gfn_t gfn)
> if (slot)
> return slot;
>
> - slot = search_memslots(slots, gfn, &slot_index);
> + slot = search_memslots(slots, gfn, &slot_index, approx);
> if (slot) {
> atomic_set(&slots->last_used_slot, slot_index);
> return slot;
> @@ -1286,6 +1299,12 @@ __gfn_to_memslot(struct kvm_memslots *slots, gfn_t gfn)
> return NULL;
> }
>
> +static inline struct kvm_memory_slot *
> +__gfn_to_memslot(struct kvm_memslots *slots, gfn_t gfn)
> +{
> + return __gfn_to_memslot_approx(slots, gfn, false);
> +}
> +
> static inline unsigned long
> __gfn_to_hva_memslot(const struct kvm_memory_slot *slot, gfn_t gfn)
> {
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 207306f7c559..03ef42d2e421 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2074,7 +2074,7 @@ struct kvm_memory_slot *kvm_vcpu_gfn_to_memslot(struct kvm_vcpu *vcpu, gfn_t gfn
> * search_memslots() instead of __gfn_to_memslot() to avoid
> * thrashing the VM-wide last_used_index in kvm_memslots.
> */
> - slot = search_memslots(slots, gfn, &slot_index);
> + slot = search_memslots(slots, gfn, &slot_index, false);
> if (slot) {
> vcpu->last_used_slot = slot_index;
> return slot;
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