linux-kernel - Re: [PATCH v6 7/8] KVM: Enable and expose KVM_MEM

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Date:   Fri, 24 Jun 2022 16:43:41 +0800
From:   Chao Peng <chao.p.peng@...ux.intel.com>
To:     Michael Roth <michael.roth@....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>,
        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>, mhocko@...e.com
Subject: Re: [PATCH v6 7/8] KVM: Enable and expose KVM_MEM_PRIVATE

On Thu, Jun 23, 2022 at 05:07:51PM -0500, Michael Roth wrote:
...
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index db9d39a2d3a6..f93ac7cdfb53 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -843,6 +843,73 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)
> >  
> >  #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */
> >  
> > +#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM
> > +static void kvm_private_mem_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),
> 
> This code assumes that 'end' is greater than slot->private_offset, but
> even if slot->private_offset is non-zero, nothing stops userspace from
> allocating pages in the range of 0 through slot->private_offset, which
> will still end up triggering this notifier. In that case gfn_range.end
> will end up going negative, and the below code will limit that to
> slot->npages and do a populate/invalidate for the entire range.
> 
> Not sure if this covers all the cases, but this fixes the issue for me:

Right, already noticed this issue, will fix in next version. Thanks.

> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 903ffdb5f01c..4c744d8f7527 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -872,6 +872,19 @@ static void kvm_private_mem_notifier_handler(struct memfile_notifier *notifier,
>                 .may_block      = true,
>         };
> 
>         struct kvm *kvm = slot->kvm;
> +
> +       if (slot->private_offset > end)
> +               return;
> +
>