linux-kernel - Re: [PATCH v8 2/8] KVM: Extend the memslot to support fd-based private memory

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Message-ID: <20220926140451.GA2658254@chaop.bj.intel.com>
Date:   Mon, 26 Sep 2022 22:04:51 +0800
From:   Chao Peng <chao.p.peng@...ux.intel.com>
To:     Fuad Tabba <tabba@...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, 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>,
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        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 2/8] KVM: Extend the memslot to support fd-based
 private memory

On Mon, Sep 26, 2022 at 11:26:45AM +0100, Fuad Tabba wrote:
...

> > +
> > +- KVM_MEM_PRIVATE can be set to indicate a new slot has private memory backed by
> > +  a file descirptor(fd) and the content of the private memory is invisible to
> 
> s/descirptor/descriptor

Thanks.

...

>  static long kvm_vm_ioctl(struct file *filp,
> >                            unsigned int ioctl, unsigned long arg)
> >  {
> > @@ -4645,14 +4672,20 @@ static long kvm_vm_ioctl(struct file *filp,
> >                 break;
> >         }
> >         case KVM_SET_USER_MEMORY_REGION: {
> > -               struct kvm_userspace_memory_region kvm_userspace_mem;
> > +               struct kvm_user_mem_region mem;
> > +               unsigned long size = sizeof(struct kvm_userspace_memory_region);
> 
> nit: should this be sizeof(struct mem)? That's more similar to the
> existing code and makes it dependent on the size of mem regardless of
> possible changes to its type in the future.

Unluckily no, the size we need copy_from_user() depends on the flags,
e.g. without KVM_MEM_PRIVATE, we can't safely copy that big size since
the 'extended' part may not even exist.

> 
> > +
> > +               kvm_sanity_check_user_mem_region_alias();
> >
> >                 r = -EFAULT;
> > -               if (copy_from_user(&kvm_userspace_mem, argp,
> > -                                               sizeof(kvm_userspace_mem)))
> > +               if (copy_from_user(&mem, argp, size);
> 
> It gets fixed in a future patch, but the ; should be a ).

Good catch, thanks!

Chao
> 
> Cheers,
> /fuad