linux-kernel - Re: [PATCH v7 11/14] KVM: Register/unregister the guest private memory regions

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Message-ID: <20220824103738.GA1386620@chaop.bj.intel.com>
Date:   Wed, 24 Aug 2022 18:37:38 +0800
From:   Chao Peng <chao.p.peng@...ux.intel.com>
To:     Vishal Annapurve <vannapurve@...gle.com>
Cc:     kvm list <kvm@...r.kernel.org>,
        LKML <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,
        linux-kselftest@...r.kernel.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 <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>,
        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 <dave.hansen@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        David Hildenbrand <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>
Subject: Re: [PATCH v7 11/14] KVM: Register/unregister the guest private
 memory regions

On Fri, Aug 19, 2022 at 12:37:42PM -0700, Vishal Annapurve wrote:
> > ...
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 230c8ff9659c..bb714c2a4b06 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -914,6 +914,35 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)
> >
> >  #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */
> >
> > +#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM
> > +#define KVM_MEM_ATTR_PRIVATE   0x0001
> > +static int kvm_vm_ioctl_set_encrypted_region(struct kvm *kvm, unsigned int ioctl,
> > +                                            struct kvm_enc_region *region)
> > +{
> > +       unsigned long start, end;
> > +       void *entry;
> > +       int r;
> > +
> > +       if (region->size == 0 || region->addr + region->size < region->addr)
> > +               return -EINVAL;
> > +       if (region->addr & (PAGE_SIZE - 1) || region->size & (PAGE_SIZE - 1))
> > +               return -EINVAL;
> > +
> > +       start = region->addr >> PAGE_SHIFT;
> > +       end = (region->addr + region->size - 1) >> PAGE_SHIFT;
> > +
> > +       entry = ioctl == KVM_MEMORY_ENCRYPT_REG_REGION ?
> > +                               xa_mk_value(KVM_MEM_ATTR_PRIVATE) : NULL;
> > +
> > +       r = xa_err(xa_store_range(&kvm->mem_attr_array, start, end,
> > +                                       entry, GFP_KERNEL_ACCOUNT));
> 
> xa_store_range seems to create multi-index entries by default.
> Subsequent xa_store_range call changes all the entries stored
> previously.

By using xa_store_range and storing them as multi-index entries I
expected to save some memory for continuous pages originally.

But sounds like the current multi-index store behaviour isn't quite
ready for our usage.

Chao
> xa_store needs to be used here instead of xa_store_range to achieve
> the intended behavior.
> 
> > +
> > +       kvm_zap_gfn_range(kvm, start, end + 1);
> > +
> > +       return r;
> > +}
> > +#endif /* CONFIG_HAVE_KVM_PRIVATE_MEM */
> > +
> > ...