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    SubjectRe: [PATCH 0/5] kvm: fix latent guest entry/exit bugs
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    On Tue, 11 Jan 2022 07:35:34 PST (-0800), mark.rutland@arm.com wrote:
    > Several architectures have latent bugs around guest entry/exit, most
    > notably:
    >
    > 1) Several architectures enable interrupts between guest_enter() and
    > guest_exit(). As this period is an RCU extended quiescent state (EQS) this
    > is unsound unless the irq entry code explicitly wakes RCU, which most
    > architectures only do for entry from usersapce or idle.
    >
    > I believe this affects: arm64, riscv, s390
    >
    > I am not sure about powerpc.
    >
    > 2) Several architectures permit instrumentation of code between
    > guest_enter() and guest_exit(), e.g. KASAN, KCOV, KCSAN, etc. As
    > instrumentation may directly o indirectly use RCU, this has the same
    > problems as with interrupts.
    >
    > I believe this affects: arm64, mips, powerpc, riscv, s390

    Moving to Atish and Anup's new email addresses, looks like MAINTAINERS
    hasn't been updated yet. I thought I remembering seeing patches getting
    picked up for these, but LMK if you guys were expecting me to send them
    along -- sorry if I misunderstood!

    >
    > 3) Several architectures do not inform lockdep and tracing that
    > interrupts are enabled during the execution of the guest, or do so in
    > an incorrect order. Generally
    > this means that logs will report IRQs being masked for much longer
    > than is actually the case, which is not ideal for debugging. I don't
    > know whether this affects the correctness of lockdep.
    >
    > I believe this affects: arm64, mips, powerpc, riscv, s390
    >
    > This was previously fixed for x86 specifically in a series of commits:
    >
    > 87fa7f3e98a1310e ("x86/kvm: Move context tracking where it belongs")
    > 0642391e2139a2c1 ("x86/kvm/vmx: Add hardirq tracing to guest enter/exit")
    > 9fc975e9efd03e57 ("x86/kvm/svm: Add hardirq tracing on guest enter/exit")
    > 3ebccdf373c21d86 ("x86/kvm/vmx: Move guest enter/exit into .noinstr.text")
    > 135961e0a7d555fc ("x86/kvm/svm: Move guest enter/exit into .noinstr.text")
    > 160457140187c5fb ("KVM: x86: Defer vtime accounting 'til after IRQ handling")
    > bc908e091b326467 ("KVM: x86: Consolidate guest enter/exit logic to common helpers")
    >
    > But other architectures were left broken, and the infrastructure for
    > handling this correctly is x86-specific.
    >
    > This series introduces generic helper functions which can be used to
    > handle the problems above, and migrates architectures over to these,
    > fixing the latent issues.
    >
    > I wasn't able to figure my way around powerpc and s390, so I have not
    > altered these. I'd appreciate if anyone could take a look at those
    > cases, and either have a go at patches or provide some feedback as to
    > any alternative approaches which work work better there.
    >
    > I have build-tested the arm64, mips, riscv, and x86 cases, but I don't
    > have a suitable HW setup to test these, so any review and/or testing
    > would be much appreciated.
    >
    > I've pushed the series (based on v5.16) to my kvm/entry-rework branch:
    >
    > https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=kvm/entry-rework
    > git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git kvm/entry-rework
    >
    > ... also tagged as kvm-entry-rework-20210111
    >
    > Thanks,
    > Mark.
    >
    > Mark Rutland (5):
    > kvm: add exit_to_guest_mode() and enter_from_guest_mode()
    > kvm/arm64: rework guest entry logic
    > kvm/mips: rework guest entry logic
    > kvm/riscv: rework guest entry logic
    > kvm/x86: rework guest entry logic
    >
    > arch/arm64/kvm/arm.c | 51 +++++++++++-------
    > arch/mips/kvm/mips.c | 37 ++++++++++++--
    > arch/riscv/kvm/vcpu.c | 44 ++++++++++------
    > arch/x86/kvm/svm/svm.c | 4 +-
    > arch/x86/kvm/vmx/vmx.c | 4 +-
    > arch/x86/kvm/x86.c | 4 +-
    > arch/x86/kvm/x86.h | 45 ----------------
    > include/linux/kvm_host.h | 108 +++++++++++++++++++++++++++++++++++++--
    > 8 files changed, 206 insertions(+), 91 deletions(-)

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