Re: [PATCH v9 6/8] KVM: Update lpage info when private/shared memory are mixed

Chao Peng
2022-10-28T06:47:39Z

On Wed, Oct 26, 2022 at 01:46:20PM -0700, Isaku Yamahata wrote:
> On Tue, Oct 25, 2022 at 11:13:42PM +0800,
> Chao Peng <chao.p.peng@linux.intel.com> wrote:
>
> > When private/shared memory are mixed in a large page, the lpage_info may
> > not be accurate and should be updated with this mixed info. A large page
> > has mixed pages can't be really mapped as large page since its
> > private/shared pages are from different physical memory.
> >
> > Update lpage_info when private/shared memory attribute is changed. If
> > both private and shared pages are within a large page region, it can't
> > be mapped as large page. It's a bit challenge to track the mixed
> > info in a 'count' like variable, this patch instead reserves a bit in
> > 'disallow_lpage' to indicate a large page has mixed private/share pages.
> >
> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > ---
> > arch/x86/include/asm/kvm_host.h | 8 +++
> > arch/x86/kvm/mmu/mmu.c | 112 +++++++++++++++++++++++++++++++-
> > arch/x86/kvm/x86.c | 2 +
> > include/linux/kvm_host.h | 19 ++++++
> > virt/kvm/kvm_main.c | 16 +++--
> > 5 files changed, 152 insertions(+), 5 deletions(-)
> >
> ...
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 33b1aec44fb8..67a9823a8c35 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> ...
> > @@ -6910,3 +6915,108 @@ 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 inline bool linfo_is_mixed(struct kvm_lpage_info *linfo)
> > +{
> > + return linfo->disallow_lpage & KVM_LPAGE_PRIVATE_SHARED_MIXED;
> > +}
> > +
> > +static inline void linfo_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_2m(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 = attr == KVM_MEM_ATTR_SHARED;
> > + bool mixed = false;
> > +
> > + 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 && !shared) || (!entry && shared)) {
> > + mixed = true;
> > + goto out;
>
> nitpick: goto isn't needed. break should work.

Thanks.

>
> > + }
> > +
> > + entry = xas_next(&xas);
> > + gfn++;
> > + }
> > +out:
> > + rcu_read_unlock();
> > + return mixed;
> > +}
> > +
> > +static bool mem_attr_is_mixed(struct kvm *kvm, struct kvm_memory_slot *slot,
> > + int level, unsigned int attr,
> > + gfn_t start, gfn_t end)
> > +{
> > + unsigned long gfn;
> > + void *entry;
> > +
> > + if (level == PG_LEVEL_2M)
> > + return mem_attr_is_mixed_2m(kvm, attr, start, end);
> > +
> > + entry = xa_load(&kvm->mem_attr_array, start);
> > + for (gfn = start; gfn < end; gfn += KVM_PAGES_PER_HPAGE(level - 1)) {
> > + if (linfo_is_mixed(lpage_info_slot(gfn, slot, level - 1)))
> > + return true;
> > + if (xa_load(&kvm->mem_attr_array, gfn) != entry)
> > + return true;
> > + }
> > + return false;
> > +}
> > +
> > +void kvm_arch_update_mem_attr(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;
> > +
> > + WARN_ONCE(!(attr & (KVM_MEM_ATTR_PRIVATE | KVM_MEM_ATTR_SHARED)),
> > + "Unsupported mem attribute.\n");
> > +
> > + /*
> > + * The sequence matters here: we update the higher level basing on the
> > + * lower level's scanning result.
> > + */
> > + for (level = PG_LEVEL_2M; level <= KVM_MAX_HUGEPAGE_LEVEL; level++) {
> > + pages = KVM_PAGES_PER_HPAGE(level);
> > + mask = ~(pages - 1);
>
> nitpick: KVM_HPAGE_MASK(level). Maybe matter of preference.

Yes, haven't noticed there is a KVM_HPAGE_MASK defined. Have no
strong preference here, since I already have KVM_PAGES_PER_HPAGE(level),
getting mask is straightforward.

A single KVM_HPAGE_MASK(level) will not give me what I need since here
is gfn, KVM_HPAGE_MASK(level)>> PAGE_SHIFT should be the right
equivalent.

Chao
>
>
> > + lpage_start = max(start & mask, slot->base_gfn);
> > + lpage_end = (end - 1) & mask;
> > +
> > + /*
> > + * We only need to scan the head and tail page, for middle pages
> > + * we know they are not mixed.
> > + */
> > + linfo_update_mixed(lpage_info_slot(lpage_start, slot, level),
> > + mem_attr_is_mixed(kvm, slot, level, attr,
> > + lpage_start, start));
> > +
> > + if (lpage_start == lpage_end)
> > + return;
> > +
> > + for (gfn = lpage_start + pages; gfn < lpage_end; gfn += pages)
> > + linfo_update_mixed(lpage_info_slot(gfn, slot, level),
> > + false);
> > +
> > + linfo_update_mixed(lpage_info_slot(lpage_end, slot, level),
> > + mem_attr_is_mixed(kvm, slot, level, attr,
> > + end, lpage_end + pages));
> > + }
> > +}
>
> --
> Isaku Yamahata <isaku.yamahata@gmail.com>