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From:   Vipin Sharma <vipinsh@google.com>
Date:   Wed, 7 Dec 2022 14:58:00 -0800
Message-ID: <CAHVum0e3ErVfVtGXk1se+=Lr+kTFqdt8sdMDZW24zjTSADsv7w@mail.gmail.com>
Subject: Re: [PATCH 1/7] KVM: x86/MMU: Move pte_list operations to rmap.c
To:     Ben Gardon <bgardon@google.com>
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        Peter Xu <peterx@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        David Matlack <dmatlack@google.com>
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On Tue, Dec 6, 2022 at 9:36 AM Ben Gardon <bgardon@google.com> wrote:
>
> In the interest of eventually splitting the Shadow MMU out of mmu.c,
> start by moving some of the operations for manipulating pte_lists out of
> mmu.c and into a new pair of files: rmap.c and rmap.h.
>
> No functional change intended.
>
> Signed-off-by: Ben Gardon <bgardon@google.com>
> ---
>  arch/x86/kvm/Makefile           |   2 +-
>  arch/x86/kvm/debugfs.c          |   1 +
>  arch/x86/kvm/mmu/mmu.c          | 152 +-------------------------------
>  arch/x86/kvm/mmu/mmu_internal.h |   1 -
>  arch/x86/kvm/mmu/rmap.c         | 141 +++++++++++++++++++++++++++++
>  arch/x86/kvm/mmu/rmap.h         |  34 +++++++
>  6 files changed, 179 insertions(+), 152 deletions(-)
>  create mode 100644 arch/x86/kvm/mmu/rmap.c
>  create mode 100644 arch/x86/kvm/mmu/rmap.h
>
> diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
> index 80e3fe184d17..9f766eebeddf 100644
> --- a/arch/x86/kvm/Makefile
> +++ b/arch/x86/kvm/Makefile
> @@ -12,7 +12,7 @@ include $(srctree)/virt/kvm/Makefile.kvm
>  kvm-y                  += x86.o emulate.o i8259.o irq.o lapic.o \
>                            i8254.o ioapic.o irq_comm.o cpuid.o pmu.o mtrr.o \
>                            hyperv.o debugfs.o mmu/mmu.o mmu/page_track.o \
> -                          mmu/spte.o
> +                          mmu/spte.o mmu/rmap.o
>
>  ifdef CONFIG_HYPERV
>  kvm-y                  += kvm_onhyperv.o
> diff --git a/arch/x86/kvm/debugfs.c b/arch/x86/kvm/debugfs.c
> index c1390357126a..29f692ecd6f3 100644
> --- a/arch/x86/kvm/debugfs.c
> +++ b/arch/x86/kvm/debugfs.c
> @@ -9,6 +9,7 @@
>  #include "lapic.h"
>  #include "mmu.h"
>  #include "mmu/mmu_internal.h"
> +#include "mmu/rmap.h"
>
>  static int vcpu_get_timer_advance_ns(void *data, u64 *val)
>  {
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 4736d7849c60..90b3735d6064 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -26,6 +26,7 @@
>  #include "kvm_emulate.h"
>  #include "cpuid.h"
>  #include "spte.h"
> +#include "rmap.h"
>
>  #include <linux/kvm_host.h>
>  #include <linux/types.h>
> @@ -112,24 +113,6 @@ module_param(dbg, bool, 0644);
>
>  #include <trace/events/kvm.h>
>
> -/* make pte_list_desc fit well in cache lines */
> -#define PTE_LIST_EXT 14
> -
> -/*
> - * Slight optimization of cacheline layout, by putting `more' and `spte_count'
> - * at the start; then accessing it will only use one single cacheline for
> - * either full (entries==PTE_LIST_EXT) case or entries<=6.
> - */
> -struct pte_list_desc {
> -       struct pte_list_desc *more;
> -       /*
> -        * Stores number of entries stored in the pte_list_desc.  No need to be
> -        * u64 but just for easier alignment.  When PTE_LIST_EXT, means full.
> -        */
> -       u64 spte_count;
> -       u64 *sptes[PTE_LIST_EXT];
> -};
> -
>  struct kvm_shadow_walk_iterator {
>         u64 addr;
>         hpa_t shadow_addr;
> @@ -155,7 +138,6 @@ struct kvm_shadow_walk_iterator {
>                 ({ spte = mmu_spte_get_lockless(_walker.sptep); 1; });  \
>              __shadow_walk_next(&(_walker), spte))
>
> -static struct kmem_cache *pte_list_desc_cache;
>  struct kmem_cache *mmu_page_header_cache;
>  static struct percpu_counter kvm_total_used_mmu_pages;
>
> @@ -674,11 +656,6 @@ static void mmu_free_memory_caches(struct kvm_vcpu *vcpu)
>         kvm_mmu_free_memory_cache(&vcpu->arch.mmu_page_header_cache);
>  }
>
> -static void mmu_free_pte_list_desc(struct pte_list_desc *pte_list_desc)
> -{
> -       kmem_cache_free(pte_list_desc_cache, pte_list_desc);
> -}
> -
>  static bool sp_has_gptes(struct kvm_mmu_page *sp);
>
>  static gfn_t kvm_mmu_page_get_gfn(struct kvm_mmu_page *sp, int index)
> @@ -878,111 +855,6 @@ gfn_to_memslot_dirty_bitmap(struct kvm_vcpu *vcpu, gfn_t gfn,
>         return slot;
>  }
>
> -/*
> - * About rmap_head encoding:
> - *
> - * If the bit zero of rmap_head->val is clear, then it points to the only spte
> - * in this rmap chain. Otherwise, (rmap_head->val & ~1) points to a struct
> - * pte_list_desc containing more mappings.
> - */
> -
> -/*
> - * Returns the number of pointers in the rmap chain, not counting the new one.
> - */
> -static int pte_list_add(struct kvm_mmu_memory_cache *cache, u64 *spte,
> -                       struct kvm_rmap_head *rmap_head)
> -{
> -       struct pte_list_desc *desc;
> -       int count = 0;
> -
> -       if (!rmap_head->val) {
> -               rmap_printk("%p %llx 0->1\n", spte, *spte);
> -               rmap_head->val = (unsigned long)spte;
> -       } else if (!(rmap_head->val & 1)) {
> -               rmap_printk("%p %llx 1->many\n", spte, *spte);
> -               desc = kvm_mmu_memory_cache_alloc(cache);
> -               desc->sptes[0] = (u64 *)rmap_head->val;
> -               desc->sptes[1] = spte;
> -               desc->spte_count = 2;
> -               rmap_head->val = (unsigned long)desc | 1;
> -               ++count;
> -       } else {
> -               rmap_printk("%p %llx many->many\n", spte, *spte);
> -               desc = (struct pte_list_desc *)(rmap_head->val & ~1ul);
> -               while (desc->spte_count == PTE_LIST_EXT) {
> -                       count += PTE_LIST_EXT;
> -                       if (!desc->more) {
> -                               desc->more = kvm_mmu_memory_cache_alloc(cache);
> -                               desc = desc->more;
> -                               desc->spte_count = 0;
> -                               break;
> -                       }
> -                       desc = desc->more;
> -               }
> -               count += desc->spte_count;
> -               desc->sptes[desc->spte_count++] = spte;
> -       }
> -       return count;
> -}
> -
> -static void
> -pte_list_desc_remove_entry(struct kvm_rmap_head *rmap_head,
> -                          struct pte_list_desc *desc, int i,
> -                          struct pte_list_desc *prev_desc)
> -{
> -       int j = desc->spte_count - 1;
> -
> -       desc->sptes[i] = desc->sptes[j];
> -       desc->sptes[j] = NULL;
> -       desc->spte_count--;
> -       if (desc->spte_count)
> -               return;
> -       if (!prev_desc && !desc->more)
> -               rmap_head->val = 0;
> -       else
> -               if (prev_desc)
> -                       prev_desc->more = desc->more;
> -               else
> -                       rmap_head->val = (unsigned long)desc->more | 1;
> -       mmu_free_pte_list_desc(desc);
> -}
> -
> -static void pte_list_remove(u64 *spte, struct kvm_rmap_head *rmap_head)
> -{
> -       struct pte_list_desc *desc;
> -       struct pte_list_desc *prev_desc;
> -       int i;
> -
> -       if (!rmap_head->val) {
> -               pr_err("%s: %p 0->BUG\n", __func__, spte);
> -               BUG();
> -       } else if (!(rmap_head->val & 1)) {
> -               rmap_printk("%p 1->0\n", spte);
> -               if ((u64 *)rmap_head->val != spte) {
> -                       pr_err("%s:  %p 1->BUG\n", __func__, spte);
> -                       BUG();
> -               }
> -               rmap_head->val = 0;
> -       } else {
> -               rmap_printk("%p many->many\n", spte);
> -               desc = (struct pte_list_desc *)(rmap_head->val & ~1ul);
> -               prev_desc = NULL;
> -               while (desc) {
> -                       for (i = 0; i < desc->spte_count; ++i) {
> -                               if (desc->sptes[i] == spte) {
> -                                       pte_list_desc_remove_entry(rmap_head,
> -                                                       desc, i, prev_desc);
> -                                       return;
> -                               }
> -                       }
> -                       prev_desc = desc;
> -                       desc = desc->more;
> -               }
> -               pr_err("%s: %p many->many\n", __func__, spte);
> -               BUG();
> -       }
> -}
> -
>  static void kvm_zap_one_rmap_spte(struct kvm *kvm,
>                                   struct kvm_rmap_head *rmap_head, u64 *sptep)
>  {
> @@ -1011,7 +883,7 @@ static bool kvm_zap_all_rmap_sptes(struct kvm *kvm,
>                 for (i = 0; i < desc->spte_count; i++)
>                         mmu_spte_clear_track_bits(kvm, desc->sptes[i]);
>                 next = desc->more;
> -               mmu_free_pte_list_desc(desc);
> +               free_pte_list_desc(desc);
>         }
>  out:
>         /* rmap_head is meaningless now, remember to reset it */
> @@ -1019,26 +891,6 @@ static bool kvm_zap_all_rmap_sptes(struct kvm *kvm,
>         return true;
>  }
>
> -unsigned int pte_list_count(struct kvm_rmap_head *rmap_head)
> -{
> -       struct pte_list_desc *desc;
> -       unsigned int count = 0;
> -
> -       if (!rmap_head->val)
> -               return 0;
> -       else if (!(rmap_head->val & 1))
> -               return 1;
> -
> -       desc = (struct pte_list_desc *)(rmap_head->val & ~1ul);
> -
> -       while (desc) {
> -               count += desc->spte_count;
> -               desc = desc->more;
> -       }
> -
> -       return count;
> -}
> -
>  static struct kvm_rmap_head *gfn_to_rmap(gfn_t gfn, int level,
>                                          const struct kvm_memory_slot *slot)
>  {
> diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
> index dbaf6755c5a7..cd1c8f32269d 100644
> --- a/arch/x86/kvm/mmu/mmu_internal.h
> +++ b/arch/x86/kvm/mmu/mmu_internal.h
> @@ -166,7 +166,6 @@ bool kvm_mmu_slot_gfn_write_protect(struct kvm *kvm,
>                                     int min_level);
>  void kvm_flush_remote_tlbs_with_address(struct kvm *kvm,
>                                         u64 start_gfn, u64 pages);
> -unsigned int pte_list_count(struct kvm_rmap_head *rmap_head);
>
>  extern int nx_huge_pages;
>  static inline bool is_nx_huge_page_enabled(struct kvm *kvm)
> diff --git a/arch/x86/kvm/mmu/rmap.c b/arch/x86/kvm/mmu/rmap.c
> new file mode 100644
> index 000000000000..daa99dee0709
> --- /dev/null
> +++ b/arch/x86/kvm/mmu/rmap.c
> @@ -0,0 +1,141 @@
> +// SPDX-License-Identifier: GPL-2.0
> +

A comment would be nice to write expectations from this file and what
code lives here.

> +#include "mmu.h"
> +#include "mmu_internal.h"
> +#include "mmutrace.h"
> +#include "rmap.h"
> +#include "spte.h"
> +
> +#include <asm/cmpxchg.h>
> +#include <trace/events/kvm.h>
> +
> +/*
> + * About rmap_head encoding:
> + *
> + * If the bit zero of rmap_head->val is clear, then it points to the only spte
> + * in this rmap chain. Otherwise, (rmap_head->val & ~1) points to a struct
> + * pte_list_desc containing more mappings.
> + */
> +
> +/*
> + * Returns the number of pointers in the rmap chain, not counting the new one.
> + */
> +int pte_list_add(struct kvm_mmu_memory_cache *cache, u64 *spte,
> +                struct kvm_rmap_head *rmap_head)
> +{
> +       struct pte_list_desc *desc;
> +       int count = 0;
> +
> +       if (!rmap_head->val) {
> +               rmap_printk("%p %llx 0->1\n", spte, *spte);
> +               rmap_head->val = (unsigned long)spte;
> +       } else if (!(rmap_head->val & 1)) {
> +               rmap_printk("%p %llx 1->many\n", spte, *spte);
> +               desc = kvm_mmu_memory_cache_alloc(cache);
> +               desc->sptes[0] = (u64 *)rmap_head->val;
> +               desc->sptes[1] = spte;
> +               desc->spte_count = 2;
> +               rmap_head->val = (unsigned long)desc | 1;
> +               ++count;
> +       } else {
> +               rmap_printk("%p %llx many->many\n", spte, *spte);
> +               desc = (struct pte_list_desc *)(rmap_head->val & ~1ul);
> +               while (desc->spte_count == PTE_LIST_EXT) {
> +                       count += PTE_LIST_EXT;
> +                       if (!desc->more) {
> +                               desc->more = kvm_mmu_memory_cache_alloc(cache);
> +                               desc = desc->more;
> +                               desc->spte_count = 0;
> +                               break;
> +                       }
> +                       desc = desc->more;
> +               }
> +               count += desc->spte_count;
> +               desc->sptes[desc->spte_count++] = spte;
> +       }
> +       return count;
> +}
> +
> +void free_pte_list_desc(struct pte_list_desc *pte_list_desc)
> +{
> +       kmem_cache_free(pte_list_desc_cache, pte_list_desc);
> +}
> +
> +static void
> +pte_list_desc_remove_entry(struct kvm_rmap_head *rmap_head,
> +                          struct pte_list_desc *desc, int i,
> +                          struct pte_list_desc *prev_desc)
> +{
> +       int j = desc->spte_count - 1;
> +
> +       desc->sptes[i] = desc->sptes[j];
> +       desc->sptes[j] = NULL;
> +       desc->spte_count--;
> +       if (desc->spte_count)
> +               return;
> +       if (!prev_desc && !desc->more)
> +               rmap_head->val = 0;
> +       else
> +               if (prev_desc)
> +                       prev_desc->more = desc->more;
> +               else
> +                       rmap_head->val = (unsigned long)desc->more | 1;
> +       free_pte_list_desc(desc);
> +}
> +
> +void pte_list_remove(u64 *spte, struct kvm_rmap_head *rmap_head)
> +{
> +       struct pte_list_desc *desc;
> +       struct pte_list_desc *prev_desc;
> +       int i;
> +
> +       if (!rmap_head->val) {
> +               pr_err("%s: %p 0->BUG\n", __func__, spte);
> +               BUG();
> +       } else if (!(rmap_head->val & 1)) {
> +               rmap_printk("%p 1->0\n", spte);
> +               if ((u64 *)rmap_head->val != spte) {
> +                       pr_err("%s:  %p 1->BUG\n", __func__, spte);
> +                       BUG();
> +               }
> +               rmap_head->val = 0;
> +       } else {
> +               rmap_printk("%p many->many\n", spte);
> +               desc = (struct pte_list_desc *)(rmap_head->val & ~1ul);
> +               prev_desc = NULL;
> +               while (desc) {
> +                       for (i = 0; i < desc->spte_count; ++i) {
> +                               if (desc->sptes[i] == spte) {
> +                                       pte_list_desc_remove_entry(rmap_head,
> +                                                       desc, i, prev_desc);
> +                                       return;
> +                               }
> +                       }
> +                       prev_desc = desc;
> +                       desc = desc->more;
> +               }
> +               pr_err("%s: %p many->many\n", __func__, spte);
> +               BUG();
> +       }
> +}
> +
> +unsigned int pte_list_count(struct kvm_rmap_head *rmap_head)
> +{
> +       struct pte_list_desc *desc;
> +       unsigned int count = 0;
> +
> +       if (!rmap_head->val)
> +               return 0;
> +       else if (!(rmap_head->val & 1))
> +               return 1;
> +
> +       desc = (struct pte_list_desc *)(rmap_head->val & ~1ul);
> +
> +       while (desc) {
> +               count += desc->spte_count;
> +               desc = desc->more;
> +       }
> +
> +       return count;
> +}
> +
> diff --git a/arch/x86/kvm/mmu/rmap.h b/arch/x86/kvm/mmu/rmap.h
> new file mode 100644
> index 000000000000..059765b6e066
> --- /dev/null
> +++ b/arch/x86/kvm/mmu/rmap.h
> @@ -0,0 +1,34 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#ifndef __KVM_X86_MMU_RMAP_H
> +#define __KVM_X86_MMU_RMAP_H
> +
> +#include <linux/kvm_host.h>
> +
> +/* make pte_list_desc fit well in cache lines */
> +#define PTE_LIST_EXT 14
> +
> +/*
> + * Slight optimization of cacheline layout, by putting `more' and `spte_count'
> + * at the start; then accessing it will only use one single cacheline for
> + * either full (entries==PTE_LIST_EXT) case or entries<=6.
> + */
> +struct pte_list_desc {
> +       struct pte_list_desc *more;
> +       /*
> +        * Stores number of entries stored in the pte_list_desc.  No need to be
> +        * u64 but just for easier alignment.  When PTE_LIST_EXT, means full.
> +        */
> +       u64 spte_count;
> +       u64 *sptes[PTE_LIST_EXT];
> +};
> +
> +static struct kmem_cache *pte_list_desc_cache;

Does it make sense to make it non static and extern here. Also, you
can provide an init function which can be called from mmu.c?


> +
> +int pte_list_add(struct kvm_mmu_memory_cache *cache, u64 *spte,
> +                struct kvm_rmap_head *rmap_head);
> +void free_pte_list_desc(struct pte_list_desc *pte_list_desc);
> +void pte_list_remove(u64 *spte, struct kvm_rmap_head *rmap_head);
> +unsigned int pte_list_count(struct kvm_rmap_head *rmap_head);
> +

Similar to tdp_mmu, and other rmap functions in next patches in the
series should above functions be prefixed with "rmap_"?


> +#endif /* __KVM_X86_MMU_RMAP_H */
> --
> 2.39.0.rc0.267.gcb52ba06e7-goog
>