Re: [PATCH 1/7] KVM: x86/MMU: Move pte_list operations to rmap.c

From: Ben Gardon
Date: Tue Dec 13 2022 - 19:13:39 EST

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In reply to: Ben Gardon: "Re: [PATCH 1/7] KVM: x86/MMU: Move pte_list operations to rmap.c"
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On Wed, Dec 7, 2022 at 2:58 PM Vipin Sharma <vipinsh@xxxxxxxxxx> wrote:
>
> On Tue, Dec 6, 2022 at 9:36 AM Ben Gardon <bgardon@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> > 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.

I'll add one.

>
> > +#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?

Going to follow David's suggestion and leave it in mmu.c for now.

>
>
> > +
> > +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_"?

I think I'm going to abandon the idea of having a seperate file for
rmap stuff and just have one, larger shadow mmu file with a variety of
names. I'll clean up the naming at the end of the series once
everything is moved over and the set of things being exported from the
shadow_mmu.c file has stabilized.

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

Next message: Ben Gardon: "Re: [PATCH 2/7] KVM: x86/MMU: Move rmap_iterator to rmap.h"
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