From: Chao Peng <chao.p.peng@linux.intel.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Ackerley Tng <ackerleytng@google.com>,
aarcange@redhat.com, ak@linux.intel.com,
akpm@linux-foundation.org, bfields@fieldses.org, bp@alien8.de,
corbet@lwn.net, dave.hansen@intel.com, david@redhat.com,
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hughd@google.com, jlayton@kernel.org, jmattson@google.com,
joro@8bytes.org, jun.nakajima@intel.com,
kirill.shutemov@linux.intel.com, kvm@vger.kernel.org,
linux-api@vger.kernel.org, linux-arch@vger.kernel.org,
linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
luto@kernel.org, mail@maciej.szmigiero.name, mhocko@suse.com,
michael.roth@amd.com, mingo@redhat.com, pbonzini@redhat.com,
qemu-devel@nongnu.org, qperret@google.com, rppt@kernel.org,
shuah@kernel.org, songmuchun@bytedance.com, steven.price@arm.com,
tabba@google.com, tglx@linutronix.de, vannapurve@google.com,
vbabka@suse.cz, vkuznets@redhat.com, wanpengli@tencent.com,
wei.w.wang@intel.com, x86@kernel.org, yu.c.zhang@linux.intel.com
Subject: Re: [PATCH v9 7/8] KVM: Handle page fault for private memory
Date: Thu, 17 Nov 2022 21:25:51 +0800 [thread overview]
Message-ID: <20221117132551.GB422408@chaop.bj.intel.com> (raw)
In-Reply-To: <Y3Vgc5KrNRA8r6vh@google.com>
On Wed, Nov 16, 2022 at 10:13:07PM +0000, Sean Christopherson wrote:
> On Wed, Nov 16, 2022, Ackerley Tng wrote:
> > >@@ -4173,6 +4203,22 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> > > return RET_PF_EMULATE;
> > > }
> > >
> > >+ if (kvm_slot_can_be_private(slot) &&
> > >+ fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn)) {
> > >+ vcpu->run->exit_reason = KVM_EXIT_MEMORY_FAULT;
> > >+ if (fault->is_private)
> > >+ vcpu->run->memory.flags = KVM_MEMORY_EXIT_FLAG_PRIVATE;
> > >+ else
> > >+ vcpu->run->memory.flags = 0;
> > >+ vcpu->run->memory.padding = 0;
> > >+ vcpu->run->memory.gpa = fault->gfn << PAGE_SHIFT;
> > >+ vcpu->run->memory.size = PAGE_SIZE;
> > >+ return RET_PF_USER;
> > >+ }
> > >+
> > >+ if (fault->is_private)
> > >+ return kvm_faultin_pfn_private(fault);
> > >+
> >
> > Since each memslot may also not be backed by restricted memory, we
> > should also check if the memslot has been set up for private memory
> > with
> >
> > if (fault->is_private && kvm_slot_can_be_private(slot))
> > return kvm_faultin_pfn_private(fault);
> >
> > Without this check, restrictedmem_get_page will get called with NULL
> > in slot->restricted_file, which causes a NULL pointer dereference.
>
> Hmm, silently skipping the faultin would result in KVM faulting in the shared
> portion of the memslot, and I believe would end up mapping that pfn as private,
> i.e. would map a non-UPM PFN as a private mapping. For TDX and SNP, that would
> be double ungood as it would let the host access memory that is mapped private,
> i.e. lead to #MC or #PF(RMP) in the host.
That's correct.
>
> I believe the correct solution is to drop the "can be private" check from the
> above check, and instead handle that in kvm_faultin_pfn_private(). That would fix
> another bug, e.g. if the fault is shared, the slot can't be private, but for
> whatever reason userspace marked the gfn as private. Even though KVM might be
> able service the fault, the correct thing to do in that case is to exit to userspace.
It makes sense to me.
Chao
>
> E.g.
>
> ---
> arch/x86/kvm/mmu/mmu.c | 36 ++++++++++++++++++++++--------------
> 1 file changed, 22 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 10017a9f26ee..e2ac8873938e 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4158,11 +4158,29 @@ static inline u8 order_to_level(int order)
> return PG_LEVEL_4K;
> }
>
> -static int kvm_faultin_pfn_private(struct kvm_page_fault *fault)
> +static int kvm_do_memory_fault_exit(struct kvm_vcpu *vcpu,
> + struct kvm_page_fault *fault)
> +{
> + vcpu->run->exit_reason = KVM_EXIT_MEMORY_FAULT;
> + if (fault->is_private)
> + vcpu->run->memory.flags = KVM_MEMORY_EXIT_FLAG_PRIVATE;
> + else
> + vcpu->run->memory.flags = 0;
> + vcpu->run->memory.padding = 0;
> + vcpu->run->memory.gpa = fault->gfn << PAGE_SHIFT;
> + vcpu->run->memory.size = PAGE_SIZE;
> + return RET_PF_USER;
> +}
> +
> +static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
> + struct kvm_page_fault *fault)
> {
> int order;
> struct kvm_memory_slot *slot = fault->slot;
>
> + if (kvm_slot_can_be_private(slot))
> + return kvm_do_memory_fault_exit(vcpu, fault);
> +
> if (kvm_restricted_mem_get_pfn(slot, fault->gfn, &fault->pfn, &order))
> return RET_PF_RETRY;
>
> @@ -4203,21 +4221,11 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> return RET_PF_EMULATE;
> }
>
> - if (kvm_slot_can_be_private(slot) &&
> - fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn)) {
> - vcpu->run->exit_reason = KVM_EXIT_MEMORY_FAULT;
> - if (fault->is_private)
> - vcpu->run->memory.flags = KVM_MEMORY_EXIT_FLAG_PRIVATE;
> - else
> - vcpu->run->memory.flags = 0;
> - vcpu->run->memory.padding = 0;
> - vcpu->run->memory.gpa = fault->gfn << PAGE_SHIFT;
> - vcpu->run->memory.size = PAGE_SIZE;
> - return RET_PF_USER;
> - }
> + if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn))
> + return kvm_do_memory_fault_exit(vcpu, fault);
>
> if (fault->is_private)
> - return kvm_faultin_pfn_private(fault);
> + return kvm_faultin_pfn_private(vcpu, fault);
>
> async = false;
> fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, &async,
>
> base-commit: 969d761bb7b8654605937f31ae76123dcb7f15a3
> --
next prev parent reply other threads:[~2022-11-17 13:30 UTC|newest]
Thread overview: 101+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-25 15:13 [PATCH v9 0/8] KVM: mm: fd-based approach for supporting KVM Chao Peng
2022-10-25 15:13 ` [PATCH v9 1/8] mm: Introduce memfd_restricted system call to create restricted user memory Chao Peng
2022-10-26 17:31 ` Isaku Yamahata
2022-10-28 6:12 ` Chao Peng
2022-10-27 10:20 ` Fuad Tabba
2022-10-31 17:47 ` Michael Roth
2022-11-01 11:37 ` Chao Peng
2022-11-01 15:19 ` Michael Roth
2022-11-01 19:30 ` Michael Roth
2022-11-02 14:53 ` Chao Peng
2022-11-02 21:19 ` Michael Roth
2022-11-14 14:02 ` Vlastimil Babka
2022-11-14 15:28 ` Kirill A. Shutemov
2022-11-14 22:16 ` Michael Roth
2022-11-15 9:48 ` Chao Peng
2022-11-14 22:16 ` Michael Roth
2022-11-02 21:14 ` Kirill A. Shutemov
2022-11-02 21:26 ` Michael Roth
2022-11-02 22:07 ` Michael Roth
2022-11-03 16:30 ` Kirill A. Shutemov
2022-11-29 0:06 ` Michael Roth
2022-11-29 11:21 ` Kirill A. Shutemov
2022-11-29 11:39 ` David Hildenbrand
2022-11-29 13:59 ` Chao Peng
2022-11-29 13:58 ` Chao Peng
2022-11-29 0:37 ` Michael Roth
2022-11-29 14:06 ` Chao Peng
2022-11-29 19:06 ` Michael Roth
2022-11-29 19:18 ` Michael Roth
2022-11-30 9:39 ` Chao Peng
2022-11-30 14:31 ` Michael Roth
2022-11-29 18:01 ` Vishal Annapurve
2022-12-02 2:16 ` Vishal Annapurve
2022-12-02 6:49 ` Chao Peng
2022-12-02 13:44 ` Kirill A . Shutemov
2022-10-25 15:13 ` [PATCH v9 2/8] KVM: Extend the memslot to support fd-based private memory Chao Peng
2022-10-27 10:25 ` Fuad Tabba
2022-10-28 7:04 ` Xiaoyao Li
2022-10-31 14:14 ` Chao Peng
2022-11-14 16:04 ` Alex Bennée
2022-11-15 9:29 ` Chao Peng
2022-10-25 15:13 ` [PATCH v9 3/8] KVM: Add KVM_EXIT_MEMORY_FAULT exit Chao Peng
2022-10-25 15:26 ` Peter Maydell
2022-10-25 16:17 ` Sean Christopherson
2022-10-27 10:27 ` Fuad Tabba
2022-10-28 6:14 ` Chao Peng
2022-11-15 16:56 ` Alex Bennée
2022-11-16 3:14 ` Chao Peng
2022-11-16 19:03 ` Alex Bennée
2022-11-17 13:45 ` Chao Peng
2022-11-17 15:08 ` Alex Bennée
2022-11-18 1:32 ` Chao Peng
2022-11-18 13:23 ` Alex Bennée
2022-11-18 15:59 ` Sean Christopherson
2022-11-22 9:50 ` Chao Peng
2022-11-23 18:02 ` Sean Christopherson
2022-11-16 18:15 ` Andy Lutomirski
2022-11-16 18:48 ` Sean Christopherson
2022-11-17 13:42 ` Chao Peng
2022-10-25 15:13 ` [PATCH v9 4/8] KVM: Use gfn instead of hva for mmu_notifier_retry Chao Peng
2022-10-27 10:29 ` Fuad Tabba
2022-11-04 2:28 ` Chao Peng
2022-11-04 22:29 ` Sean Christopherson
2022-11-08 7:16 ` Chao Peng
2022-11-10 17:53 ` Sean Christopherson
2022-11-10 20:06 ` Sean Christopherson
2022-11-11 8:27 ` Chao Peng
2022-10-25 15:13 ` [PATCH v9 5/8] KVM: Register/unregister the guest private memory regions Chao Peng
2022-10-27 10:31 ` Fuad Tabba
2022-11-03 23:04 ` Sean Christopherson
2022-11-04 8:28 ` Chao Peng
2022-11-04 21:19 ` Sean Christopherson
2022-11-08 8:24 ` Chao Peng
2022-11-08 1:35 ` Yuan Yao
2022-11-08 9:41 ` Chao Peng
2022-11-09 5:52 ` Yuan Yao
2022-11-16 22:24 ` Sean Christopherson
2022-11-17 13:20 ` Chao Peng
2022-10-25 15:13 ` [PATCH v9 6/8] KVM: Update lpage info when private/shared memory are mixed Chao Peng
2022-10-26 20:46 ` Isaku Yamahata
2022-10-28 6:38 ` Chao Peng
2022-11-08 12:08 ` Yuan Yao
2022-11-09 4:13 ` Chao Peng
2022-10-25 15:13 ` [PATCH v9 7/8] KVM: Handle page fault for private memory Chao Peng
2022-10-26 21:54 ` Isaku Yamahata
2022-10-28 6:55 ` Chao Peng
2022-11-01 0:02 ` Isaku Yamahata
2022-11-01 11:38 ` Chao Peng
2022-11-16 20:50 ` Ackerley Tng
2022-11-16 22:13 ` Sean Christopherson
2022-11-17 13:25 ` Chao Peng [this message]
2022-10-25 15:13 ` [PATCH v9 8/8] KVM: Enable and expose KVM_MEM_PRIVATE Chao Peng
2022-10-27 10:31 ` Fuad Tabba
2022-11-03 12:13 ` [PATCH v9 0/8] KVM: mm: fd-based approach for supporting KVM Vishal Annapurve
2022-11-08 0:41 ` Isaku Yamahata
2022-11-09 15:54 ` Kirill A. Shutemov
2022-11-15 14:36 ` Kirill A. Shutemov
2022-11-14 11:43 ` Alex Bennée
2022-11-16 5:00 ` Chao Peng
2022-11-16 9:40 ` Alex Bennée
2022-11-17 14:16 ` Chao Peng
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