From: Peter Xu <peterx@redhat.com>
To: Gavin Shan <gshan@redhat.com>
Cc: kvmarm@lists.linux.dev, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, pbonzini@redhat.com,
maz@kernel.org, seanjc@google.com, oliver.upton@linux.dev,
aarcange@redhat.com, david@redhat.com, hshuai@redhat.com,
zhenyzha@redhat.com, shan.gavin@gmail.com
Subject: Re: [PATCH v2] KVM: Avoid illegal stage2 mapping on invalid memory slot
Date: Fri, 9 Jun 2023 14:04:00 -0400 [thread overview]
Message-ID: <ZINpkOCYoDBQYhdq@x1n> (raw)
In-Reply-To: <20230609100420.521351-1-gshan@redhat.com>
On Fri, Jun 09, 2023 at 08:04:20PM +1000, Gavin Shan wrote:
> We run into guest hang in edk2 firmware when KSM is kept as running on
> the host. The edk2 firmware is waiting for status 0x80 from QEMU's pflash
> device (TYPE_PFLASH_CFI01) during the operation of sector erasing or
> buffered write. The status is returned by reading the memory region of
> the pflash device and the read request should have been forwarded to QEMU
> and emulated by it. Unfortunately, the read request is covered by an
> illegal stage2 mapping when the guest hang issue occurs. The read request
> is completed with QEMU bypassed and wrong status is fetched. The edk2
> firmware runs into an infinite loop with the wrong status.
>
> The illegal stage2 mapping is populated due to same page sharing by KSM
> at (C) even the associated memory slot has been marked as invalid at (B)
> when the memory slot is requested to be deleted. It's notable that the
> active and inactive memory slots can't be swapped when we're in the middle
> of kvm_mmu_notifier_change_pte() because kvm->mn_active_invalidate_count
> is elevated, and kvm_swap_active_memslots() will busy loop until it reaches
> to zero again. Besides, the swapping from the active to the inactive memory
> slots is also avoided by holding &kvm->srcu in __kvm_handle_hva_range(),
> corresponding to synchronize_srcu_expedited() in kvm_swap_active_memslots().
>
> CPU-A CPU-B
> ----- -----
> ioctl(kvm_fd, KVM_SET_USER_MEMORY_REGION)
> kvm_vm_ioctl_set_memory_region
> kvm_set_memory_region
> __kvm_set_memory_region
> kvm_set_memslot(kvm, old, NULL, KVM_MR_DELETE)
> kvm_invalidate_memslot
> kvm_copy_memslot
> kvm_replace_memslot
> kvm_swap_active_memslots (A)
> kvm_arch_flush_shadow_memslot (B)
> same page sharing by KSM
> kvm_mmu_notifier_invalidate_range_start
> :
> kvm_mmu_notifier_change_pte
> kvm_handle_hva_range
> __kvm_handle_hva_range (C)
> :
> kvm_mmu_notifier_invalidate_range_end
>
> Fix the issue by skipping the invalid memory slot at (C) to avoid the
> illegal stage2 mapping so that the read request for the pflash's status
> is forwarded to QEMU and emulated by it. In this way, the correct pflash's
> status can be returned from QEMU to break the infinite loop in the edk2
> firmware.
>
> Cc: stable@vger.kernel.org # v5.13+
> Fixes: 3039bcc74498 ("KVM: Move x86's MMU notifier memslot walkers to generic code")
> Reported-by: Shuai Hu <hshuai@redhat.com>
> Reported-by: Zhenyu Zhang <zhenyzha@redhat.com>
> Signed-off-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
--
Peter Xu
next prev parent reply other threads:[~2023-06-09 18:04 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-09 10:04 [PATCH v2] KVM: Avoid illegal stage2 mapping on invalid memory slot Gavin Shan
2023-06-09 12:53 ` Marc Zyngier
2023-06-09 18:04 ` Peter Xu [this message]
2023-06-12 1:59 ` Shaoqin Huang
2023-06-12 7:11 ` David Hildenbrand
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