linux-kernel - Re: "KVM: x86/mmu: Overhaul TDP MMU zapping and flushing" breaks SVM on Hyper-V

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Message-ID: <88a89319-a71e-fa90-0dbb-00cf8a549380@redhat.com>
Date:   Mon, 13 Feb 2023 13:50:12 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Tianyu Lan <ltykernel@...il.com>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
Subject: Re: "KVM: x86/mmu: Overhaul TDP MMU zapping and flushing" breaks SVM
 on Hyper-V


On 2/13/23 13:44, Jeremi Piotrowski wrote:
> Just built a kernel from that tree, and it displays the same behavior. The problem
> is not that the addresses are wrong, but that the flushes are issued at the wrong
> time now. At least for what "enlightened NPT TLB flush" requires.

It is not clear to me why HvCallFluyshGuestPhysicalAddressSpace or 
HvCallFlushGuestPhysicalAddressList would have stricter requirements 
than a "regular" TLB shootdown using INVEPT.

Can you clarify what you mean by wrong time, preferrably with some kind 
of sequence of events?

That is, something like

CPU 0	Modify EPT from ... to ...
CPU 0	call_rcu() to free page table
CPU 1	... which is invalid because ...
CPU 0	HvCallFlushGuestPhysicalAddressSpace

Paolo