Messages in this thread | | | Date | Tue, 11 Jan 2022 10:47:38 -0800 (PST) | Subject | Re: [PATCH 0/5] kvm: fix latent guest entry/exit bugs | From | Palmer Dabbelt <> |
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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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