linux-kernel - Re: [PATCH v6 4/8] KVM: Extend the memslot to support fd-based private memory

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20220620140941.GB2016793@chaop.bj.intel.com>
Date:   Mon, 20 Jun 2022 22:09:41 +0800
From:   Chao Peng <chao.p.peng@...ux.intel.com>
To:     Sean Christopherson <seanjc@...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>,
        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>,
        Michael Roth <michael.roth@....com>, mhocko@...e.com
Subject: Re: [PATCH v6 4/8] KVM: Extend the memslot to support fd-based
 private memory

On Fri, Jun 17, 2022 at 09:27:25PM +0000, Sean Christopherson wrote:
> On Fri, Jun 17, 2022, Sean Christopherson wrote:
> > > @@ -110,6 +133,7 @@ struct kvm_userspace_memory_region {
> > >   */
> > >  #define KVM_MEM_LOG_DIRTY_PAGES	(1UL << 0)
> > >  #define KVM_MEM_READONLY	(1UL << 1)
> > > +#define KVM_MEM_PRIVATE		(1UL << 2)
> > 
> > Hmm, KVM_MEM_PRIVATE is technically wrong now that a "private" memslot maps private
> > and/or shared memory.  Strictly speaking, we don't actually need a new flag.  Valid
> > file descriptors must be >=0, so the logic for specifying a memslot that can be
> > converted between private and shared could be that "(int)private_fd < 0" means
> > "not convertible", i.e. derive the flag from private_fd.
> > 
> > And looking at the two KVM consumers of the flag, via kvm_slot_is_private(), they're
> > both wrong.  Both kvm_faultin_pfn() and kvm_mmu_max_mapping_level() should operate
> > on the _fault_, not the slot.  So it would actually be a positive to not have an easy
> > way to query if a slot supports conversion.
> 
> I take that back, the usage in kvm_faultin_pfn() is correct, but the names ends
> up being confusing because it suggests that it always faults in a private pfn.

Make sense, will change the naming, thanks.

> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index b6d75016e48c..e1008f00609d 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4045,7 +4045,7 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
>                         return RET_PF_EMULATE;
>         }
> 
> -       if (fault->is_private) {
> +       if (kvm_slot_can_be_private(slot)) {
>                 r = kvm_faultin_pfn_private(vcpu, fault);
>                 if (r != RET_PF_CONTINUE)
>                         return r == RET_PF_FIXED ? RET_PF_CONTINUE : r;
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 31f704c83099..c5126190fb71 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -583,9 +583,9 @@ struct kvm_memory_slot {
>         struct kvm *kvm;
>  };
> 
> -static inline bool kvm_slot_is_private(const struct kvm_memory_slot *slot)
> +static inline bool kvm_slot_can_be_private(const struct kvm_memory_slot *slot)
>  {
> -       return slot && (slot->flags & KVM_MEM_PRIVATE);
> +       return slot && !!slot->private_file;
>  }
> 
>  static inline bool kvm_slot_dirty_track_enabled(const struct kvm_memory_slot *slot)