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Date: Wed, 20 Apr 2022 11:17:18 +0800
From: Chao Peng <chao.p.peng@...ux.intel.com>
To: Vishal Annapurve <vannapurve@...gle.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, 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>,
Mike Rapoport <rppt@...nel.org>,
Steven Price <steven.price@....com>,
"Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
Vlastimil Babka <vbabka@...e.cz>,
Yu Zhang <yu.c.zhang@...ux.intel.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Andy Lutomirski <luto@...nel.org>,
Jun Nakajima <jun.nakajima@...el.com>, dave.hansen@...el.com,
ak@...ux.intel.com, david@...hat.com
Subject: Re: [PATCH v5 11/13] KVM: Zap existing KVM mappings when pages
changed in the private fd
On Tue, Apr 19, 2022 at 03:43:56PM -0700, Vishal Annapurve wrote:
> On Thu, Mar 10, 2022 at 6:11 AM Chao Peng <chao.p.peng@...ux.intel.com> wrote:
> >
> > KVM gets notified when memory pages changed in the memory backing store.
> > When userspace allocates the memory with fallocate() or frees memory
> > with fallocate(FALLOC_FL_PUNCH_HOLE), memory backing store calls into
> > KVM fallocate/invalidate callbacks respectively. To ensure KVM never
> > maps both the private and shared variants of a GPA into the guest, in
> > the fallocate callback, we should zap the existing shared mapping and
> > in the invalidate callback we should zap the existing private mapping.
> >
> > In the callbacks, KVM firstly converts the offset range into the
> > gfn_range and then calls existing kvm_unmap_gfn_range() which will zap
> > the shared or private mapping. Both callbacks pass in a memslot
> > reference but we need 'kvm' so add a reference in memslot structure.
> >
> > Signed-off-by: Yu Zhang <yu.c.zhang@...ux.intel.com>
> > Signed-off-by: Chao Peng <chao.p.peng@...ux.intel.com>
> > ---
> > include/linux/kvm_host.h | 3 ++-
> > virt/kvm/kvm_main.c | 36 ++++++++++++++++++++++++++++++++++++
> > 2 files changed, 38 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 9b175aeca63f..186b9b981a65 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -236,7 +236,7 @@ bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> > int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
> > #endif
> >
> > -#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
> > +#if defined(KVM_ARCH_WANT_MMU_NOTIFIER) || defined(CONFIG_MEMFILE_NOTIFIER)
> > struct kvm_gfn_range {
> > struct kvm_memory_slot *slot;
> > gfn_t start;
> > @@ -568,6 +568,7 @@ struct kvm_memory_slot {
> > loff_t private_offset;
> > struct memfile_pfn_ops *pfn_ops;
> > struct memfile_notifier notifier;
> > + struct kvm *kvm;
> > };
> >
> > static inline bool kvm_slot_is_private(const struct kvm_memory_slot *slot)
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 67349421eae3..52319f49d58a 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -841,8 +841,43 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)
> > #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */
> >
> > #ifdef CONFIG_MEMFILE_NOTIFIER
> > +static void kvm_memfile_notifier_handler(struct memfile_notifier *notifier,
> > + pgoff_t start, pgoff_t end)
> > +{
> > + int idx;
> > + struct kvm_memory_slot *slot = container_of(notifier,
> > + struct kvm_memory_slot,
> > + notifier);
> > + struct kvm_gfn_range gfn_range = {
> > + .slot = slot,
> > + .start = start - (slot->private_offset >> PAGE_SHIFT),
> > + .end = end - (slot->private_offset >> PAGE_SHIFT),
> > + .may_block = true,
> > + };
> > + struct kvm *kvm = slot->kvm;
> > +
> > + gfn_range.start = max(gfn_range.start, slot->base_gfn);
>
> gfn_range.start seems to be page offset within the file. Should this rather be:
> gfn_range.start = slot->base_gfn + min(gfn_range.start, slot->npages);
Right. For start we don't really need care about the uppper bound
here (will check below), so this should be enough:
gfn_range.start = slot->base_gfn + gfn_range.start;
>
> > + gfn_range.end = min(gfn_range.end, slot->base_gfn + slot->npages);
> > +
>
> Similar to previous comment, should this rather be:
> gfn_range.end = slot->base_gfn + min(gfn_range.end, slot->npages);
This is correct.
Thanks,
Chao
>
> > + if (gfn_range.start >= gfn_range.end)
> > + return;
> > +
> > + idx = srcu_read_lock(&kvm->srcu);
> > + KVM_MMU_LOCK(kvm);
> > + kvm_unmap_gfn_range(kvm, &gfn_range);
> > + kvm_flush_remote_tlbs(kvm);
> > + KVM_MMU_UNLOCK(kvm);
> > + srcu_read_unlock(&kvm->srcu, idx);
> > +}
> > +
> > +static struct memfile_notifier_ops kvm_memfile_notifier_ops = {
> > + .invalidate = kvm_memfile_notifier_handler,
> > + .fallocate = kvm_memfile_notifier_handler,
> > +};
> > +
> > static inline int kvm_memfile_register(struct kvm_memory_slot *slot)
> > {
> > + slot->notifier.ops = &kvm_memfile_notifier_ops;
> > return memfile_register_notifier(file_inode(slot->private_file),
> > &slot->notifier,
> > &slot->pfn_ops);
> > @@ -1963,6 +1998,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
> > new->private_file = file;
> > new->private_offset = mem->flags & KVM_MEM_PRIVATE ?
> > region_ext->private_offset : 0;
> > + new->kvm = kvm;
> >
> > r = kvm_set_memslot(kvm, old, new, change);
> > if (!r)
> > --
> > 2.17.1
> >
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