Messages in this thread | | | Subject | Re: [PATCH v2] KVM: x86/MMU: Do not check unsync status for root SP. | From | Paolo Bonzini <> | Date | Tue, 9 Feb 2021 08:46:42 +0100 |
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On 09/02/21 04:33, Yu Zhang wrote: > On Mon, Feb 08, 2021 at 05:47:22PM +0100, Paolo Bonzini wrote: >> On 08/02/21 14:49, Yu Zhang wrote: >>> On Mon, Feb 08, 2021 at 12:36:57PM +0100, Paolo Bonzini wrote: >>>> On 07/02/21 13:22, Yu Zhang wrote: >>>>> In shadow page table, only leaf SPs may be marked as unsync. >>>>> And for non-leaf SPs, we use unsync_children to keep the number >>>>> of the unsynced children. In kvm_mmu_sync_root(), sp->unsync >>>>> shall always be zero for the root SP, , hence no need to check >>>>> it. Instead, a warning inside mmu_sync_children() is added, in >>>>> case someone incorrectly used it. >>>>> >>>>> Also, clarify the mmu_need_write_protect(), by moving the warning >>>>> into kvm_unsync_page(). >>>>> >>>>> Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com> >>>>> Signed-off-by: Sean Christopherson <seanjc@google.com> >>>> >>>> This should really be more of a Co-developed-by, and there are a couple >>>> adjustments that could be made in the commit message. I've queued the patch >>>> and I'll fix it up later. >>> >>> Indeed. Thanks for the remind, and I'll pay attention in the future. :) >> >> Also: >> >> arch/x86/kvm/mmu/mmu.c: In function ‘mmu_sync_children’: >> arch/x86/kvm/mmu/mmu.c:2002:17: error: ‘sp’ is used uninitialized in this >> function [-Werror=uninitialized] >> WARN_ON_ONCE(sp->unsync); > > Oops. This is wrong. Should be WARN_ON_ONCE(parent->unsync); > >> >> so how was this tested? >> > > I ran access test in kvm-unit-test for previous version, which hasn't > this code(also in my local repo "enable_ept" was explicitly set to > 0 in order to test the shadow mode). But I did not test this one. I'm > truely sorry for the negligence - even trying to compile should make > this happen! > > Should we submit another version? Any suggestions on the test cases?
Yes, please send v3.
The commit message can be:
In shadow page table, only leaf SPs may be marked as unsync; instead, for non-leaf SPs, we store the number of unsynced children in unsync_children. Therefore, in kvm_mmu_sync_root(), sp->unsync shall always be zero for the root SP and there is no need to check it. Remove the check, and add a warning inside mmu_sync_children() to assert that the flags are used properly.
While at it, move the warning from mmu_need_write_protect() to kvm_unsync_page().
Paolo
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