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Date: Fri, 30 Sep 2022 16:59:14 +0800
From: Chao Peng <chao.p.peng@...ux.intel.com>
To: Isaku Yamahata <isaku.yamahata@...il.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
linux-api@...r.kernel.org, linux-doc@...r.kernel.org,
qemu-devel@...gnu.org, Paolo Bonzini <pbonzini@...hat.com>,
Jonathan Corbet <corbet@....net>,
Sean Christopherson <seanjc@...gle.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
Hugh Dickins <hughd@...gle.com>,
Jeff Layton <jlayton@...nel.org>,
"J . Bruce Fields" <bfields@...ldses.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Shuah Khan <shuah@...nel.org>, Mike Rapoport <rppt@...nel.org>,
Steven Price <steven.price@....com>,
"Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
Vlastimil Babka <vbabka@...e.cz>,
Vishal Annapurve <vannapurve@...gle.com>,
Yu Zhang <yu.c.zhang@...ux.intel.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
ak@...ux.intel.com, david@...hat.com, aarcange@...hat.com,
ddutile@...hat.com, dhildenb@...hat.com,
Quentin Perret <qperret@...gle.com>,
Michael Roth <michael.roth@....com>, mhocko@...e.com,
Muchun Song <songmuchun@...edance.com>, wei.w.wang@...el.com
Subject: Re: [PATCH v8 6/8] KVM: Update lpage info when private/shared memory
are mixed
On Thu, Sep 29, 2022 at 09:52:06AM -0700, Isaku Yamahata wrote:
> On Thu, Sep 15, 2022 at 10:29:11PM +0800,
> Chao Peng <chao.p.peng@...ux.intel.com> wrote:
>
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 08abad4f3e6f..a0f198cede3d 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> ...
> > @@ -6894,3 +6899,115 @@ void kvm_mmu_pre_destroy_vm(struct kvm *kvm)
> > if (kvm->arch.nx_lpage_recovery_thread)
> > kthread_stop(kvm->arch.nx_lpage_recovery_thread);
> > }
> > +
> > +static bool mem_attr_is_mixed(struct kvm *kvm, unsigned int attr,
> > + gfn_t start, gfn_t end)
> > +{
> > + XA_STATE(xas, &kvm->mem_attr_array, start);
> > + gfn_t gfn = start;
> > + void *entry;
> > + bool shared, private;
> > + bool mixed = false;
> > +
> > + if (attr == KVM_MEM_ATTR_SHARED) {
> > + shared = true;
> > + private = false;
> > + } else {
> > + shared = false;
> > + private = true;
> > + }
>
> We don't have to care the target is shared or private. We need to check
> only same or not.
There is optimization chance if we know what we are going to set. we can
return 'mixed = true' earlier when we find the first reverse attr, e.g.
it's unnecessarily to check all the child page attr in one largepage to
give a conclusion.
After a further look, the code can be refined as below:
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -7255,17 +7255,9 @@ static bool mem_attr_is_mixed(struct kvm *kvm, unsigned int attr,
XA_STATE(xas, &kvm->mem_attr_array, start);
gfn_t gfn = start;
void *entry;
- bool shared, private;
+ bool shared = attr == KVM_MEM_ATTR_SHARED;
bool mixed = false;
- if (attr == KVM_MEM_ATTR_SHARED) {
- shared = true;
- private = false;
- } else {
- shared = false;
- private = true;
- }
-
rcu_read_lock();
entry = xas_load(&xas);
while (gfn < end) {
@@ -7274,12 +7266,7 @@ static bool mem_attr_is_mixed(struct kvm *kvm, unsigned int attr,
KVM_BUG_ON(gfn != xas.xa_index, kvm);
- if (entry)
- private = true;
- else
- shared = true;
-
- if (private && shared) {
+ if ((entry && !shared) || (!entry && shared)) {
mixed = true;
goto out;
}
@@ -7320,8 +7307,7 @@ static void update_mem_lpage_info(struct kvm *kvm,
* we know they are not mixed.
*/
update_mixed(lpage_info_slot(lpage_start, slot, level),
- mem_attr_is_mixed(kvm, attr, lpage_start,
- lpage_start + pages));
+ mem_attr_is_mixed(kvm, attr, lpage_start, start));
if (lpage_start == lpage_end)
return;
@@ -7330,7 +7316,7 @@ static void update_mem_lpage_info(struct kvm *kvm,
update_mixed(lpage_info_slot(gfn, slot, level), false);
update_mixed(lpage_info_slot(lpage_end, slot, level),
- mem_attr_is_mixed(kvm, attr, lpage_end,
+ mem_attr_is_mixed(kvm, attr, end,
lpage_end + pages));
}
}
>
> > +
> > + rcu_read_lock();
> > + entry = xas_load(&xas);
> > + while (gfn < end) {
> > + if (xas_retry(&xas, entry))
> > + continue;
> > +
> > + KVM_BUG_ON(gfn != xas.xa_index, kvm);
> > +
> > + if (entry)
> > + private = true;
> > + else
> > + shared = true;
> > +
> > + if (private && shared) {
> > + mixed = true;
> > + goto out;
> > + }
> > +
> > + entry = xas_next(&xas);
> > + gfn++;
> > + }
> > +out:
> > + rcu_read_unlock();
> > + return mixed;
> > +}
> > +
> > +static inline void update_mixed(struct kvm_lpage_info *linfo, bool mixed)
> > +{
> > + if (mixed)
> > + linfo->disallow_lpage |= KVM_LPAGE_PRIVATE_SHARED_MIXED;
> > + else
> > + linfo->disallow_lpage &= ~KVM_LPAGE_PRIVATE_SHARED_MIXED;
> > +}
> > +
> > +static void update_mem_lpage_info(struct kvm *kvm,
> > + struct kvm_memory_slot *slot,
> > + unsigned int attr,
> > + gfn_t start, gfn_t end)
> > +{
> > + unsigned long lpage_start, lpage_end;
> > + unsigned long gfn, pages, mask;
> > + int level;
> > +
> > + for (level = PG_LEVEL_2M; level <= KVM_MAX_HUGEPAGE_LEVEL; level++) {
> > + pages = KVM_PAGES_PER_HPAGE(level);
> > + mask = ~(pages - 1);
> > + lpage_start = start & mask;
> > + lpage_end = (end - 1) & mask;
> > +
> > + /*
> > + * We only need to scan the head and tail page, for middle pages
> > + * we know they are not mixed.
> > + */
> > + update_mixed(lpage_info_slot(lpage_start, slot, level),
> > + mem_attr_is_mixed(kvm, attr, lpage_start,
> > + lpage_start + pages));
> > +
> > + if (lpage_start == lpage_end)
> > + return;
> > +
> > + for (gfn = lpage_start + pages; gfn < lpage_end; gfn += pages)
> > + update_mixed(lpage_info_slot(gfn, slot, level), false);
>
>
> For >2M case, we don't have to check all entry. just check lower level case.
Sounds good, we can reduce some scanning.
Thanks,
Chao
>
> > +
> > + update_mixed(lpage_info_slot(lpage_end, slot, level),
> > + mem_attr_is_mixed(kvm, attr, lpage_end,
> > + lpage_end + pages));
> > + }
> > +}
> > +
> > +void kvm_arch_update_mem_attr(struct kvm *kvm, unsigned int attr,
> > + gfn_t start, gfn_t end)
> > +{
> > + struct kvm_memory_slot *slot;
> > + struct kvm_memslots *slots;
> > + struct kvm_memslot_iter iter;
> > + int i;
> > +
> > + WARN_ONCE(!(attr & (KVM_MEM_ATTR_PRIVATE | KVM_MEM_ATTR_SHARED)),
> > + "Unsupported mem attribute.\n");
> > +
> > + for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> > + slots = __kvm_memslots(kvm, i);
> > +
> > + kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
> > + slot = iter.slot;
> > + start = max(start, slot->base_gfn);
> > + end = min(end, slot->base_gfn + slot->npages);
> > + if (WARN_ON_ONCE(start >= end))
> > + continue;
> > +
> > + update_mem_lpage_info(kvm, slot, attr, start, end);
> > + }
> > + }
> > +}
>
>
> Here is my updated version.
>
> bool kvm_mem_attr_is_mixed(struct kvm_memory_slot *slot, gfn_t gfn, int level)
> {
> gfn_t pages = KVM_PAGES_PER_HPAGE(level);
> gfn_t mask = ~(pages - 1);
> struct kvm_lpage_info *linfo = lpage_info_slot(gfn & mask, slot, level);
>
> WARN_ON_ONCE(level == PG_LEVEL_4K);
> return linfo->disallow_lpage & KVM_LPAGE_PRIVATE_SHARED_MIXED;
> }
>
> #ifdef CONFIG_HAVE_KVM_PRIVATE_MEM_ATTR
> static void update_mixed(struct kvm_lpage_info *linfo, bool mixed)
> {
> if (mixed)
> linfo->disallow_lpage |= KVM_LPAGE_PRIVATE_SHARED_MIXED;
> else
> linfo->disallow_lpage &= ~KVM_LPAGE_PRIVATE_SHARED_MIXED;
> }
>
> static bool __mem_attr_is_mixed(struct kvm *kvm, gfn_t start, gfn_t end)
> {
> XA_STATE(xas, &kvm->mem_attr_array, start);
> bool mixed = false;
> gfn_t gfn = start;
> void *s_entry;
> void *entry;
>
> rcu_read_lock();
> s_entry = xas_load(&xas);
> entry = s_entry;
> while (gfn < end) {
> if (xas_retry(&xas, entry))
> continue;
>
> KVM_BUG_ON(gfn != xas.xa_index, kvm);
>
> entry = xas_next(&xas);
> if (entry != s_entry) {
> mixed = true;
> break;
> }
> gfn++;
> }
> rcu_read_unlock();
> return mixed;
> }
>
> static bool mem_attr_is_mixed(struct kvm *kvm,
> struct kvm_memory_slot *slot, int level,
> gfn_t start, gfn_t end)
> {
> struct kvm_lpage_info *child_linfo;
> unsigned long child_pages;
> bool mixed = false;
> unsigned long gfn;
> void *entry;
>
> if (WARN_ON_ONCE(level == PG_LEVEL_4K))
> return false;
>
> if (level == PG_LEVEL_2M)
> return __mem_attr_is_mixed(kvm, start, end);
>
> /* This assumes that level - 1 is already updated. */
> rcu_read_lock();
> child_pages = KVM_PAGES_PER_HPAGE(level - 1);
> entry = xa_load(&kvm->mem_attr_array, start);
> for (gfn = start; gfn < end; gfn += child_pages) {
> child_linfo = lpage_info_slot(gfn, slot, level - 1);
> if (child_linfo->disallow_lpage & KVM_LPAGE_PRIVATE_SHARED_MIXED) {
> mixed = true;
> break;
> }
> if (xa_load(&kvm->mem_attr_array, gfn) != entry) {
> mixed = true;
> break;
> }
> }
> rcu_read_unlock();
> return mixed;
> }
>
> static void update_mem_lpage_info(struct kvm *kvm,
> struct kvm_memory_slot *slot,
> unsigned int attr,
> gfn_t start, gfn_t end)
> {
> unsigned long lpage_start, lpage_end;
> unsigned long gfn, pages, mask;
> int level;
>
> for (level = PG_LEVEL_2M; level <= KVM_MAX_HUGEPAGE_LEVEL; level++) {
> pages = KVM_PAGES_PER_HPAGE(level);
> mask = ~(pages - 1);
> lpage_start = start & mask;
> lpage_end = (end - 1) & mask;
>
> /*
> * We only need to scan the head and tail page, for middle pages
> * we know they are not mixed.
> */
> update_mixed(lpage_info_slot(lpage_start, slot, level),
> mem_attr_is_mixed(kvm, slot, level,
> lpage_start, lpage_start + pages));
>
> if (lpage_start == lpage_end)
> return;
>
> for (gfn = lpage_start + pages; gfn < lpage_end; gfn += pages)
> update_mixed(lpage_info_slot(gfn, slot, level), false);
>
> update_mixed(lpage_info_slot(lpage_end, slot, level),
> mem_attr_is_mixed(kvm, slot, level,
> lpage_end, lpage_end + pages));
> }
> }
>
> void kvm_arch_update_mem_attr(struct kvm *kvm, unsigned int attr,
> gfn_t start, gfn_t end)
> {
> struct kvm_memory_slot *slot;
> struct kvm_memslots *slots;
> struct kvm_memslot_iter iter;
> int idx;
> int i;
>
> WARN_ONCE(!(attr & (KVM_MEM_ATTR_PRIVATE | KVM_MEM_ATTR_SHARED)),
> "Unsupported mem attribute.\n");
>
> idx = srcu_read_lock(&kvm->srcu);
> for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> slots = __kvm_memslots(kvm, i);
>
> kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
> slot = iter.slot;
> start = max(start, slot->base_gfn);
> end = min(end, slot->base_gfn + slot->npages);
> if (WARN_ON_ONCE(start >= end))
> continue;
>
> update_mem_lpage_info(kvm, slot, attr, start, end);
> }
> }
> srcu_read_unlock(&kvm->srcu, idx);
> }
> #endif
>
>
> --
> Isaku Yamahata <isaku.yamahata@...il.com>
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