linux-kernel - Re: [PATCH 0/5] KVM: rseq: Fix and a test for a KVM+rseq bug

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Date:   Wed, 22 Sep 2021 16:12:38 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Guo Ren <guoren@...nel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Shuah Khan <shuah@...nel.org>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-csky@...r.kernel.org, linux-mips@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Peter Foley <pefoley@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: Re: [PATCH 0/5] KVM: rseq: Fix and a test for a KVM+rseq bug

On 18/08/21 02:12, Sean Christopherson wrote:
> Patch 1 fixes a KVM+rseq bug where KVM's handling of TIF_NOTIFY_RESUME,
> e.g. for task migration, clears the flag without informing rseq and leads
> to stale data in userspace's rseq struct.
> 
> Patch 2 is a cleanup to try and make future bugs less likely.  It's also
> a baby step towards moving and renaming tracehook_notify_resume() since
> it has nothing to do with tracing.  It kills me to not do the move/rename
> as part of this series, but having a dedicated series/discussion seems
> more appropriate given the sheer number of architectures that call
> tracehook_notify_resume() and the lack of an obvious home for the code.
> 
> Patch 3 is a fix/cleanup to stop overriding x86's unistd_{32,64}.h when
> the include path (intentionally) omits tools' uapi headers.  KVM's
> selftests do exactly that so that they can pick up the uapi headers from
> the installed kernel headers, and still use various tools/ headers that
> mirror kernel code, e.g. linux/types.h.  This allows the new test in
> patch 4 to reference __NR_rseq without having to manually define it.
> 
> Patch 4 is a regression test for the KVM+rseq bug.
> 
> Patch 5 is a cleanup made possible by patch 3.
> 
> 
> Sean Christopherson (5):
>    KVM: rseq: Update rseq when processing NOTIFY_RESUME on xfer to KVM
>      guest
>    entry: rseq: Call rseq_handle_notify_resume() in
>      tracehook_notify_resume()
>    tools: Move x86 syscall number fallbacks to .../uapi/
>    KVM: selftests: Add a test for KVM_RUN+rseq to detect task migration
>      bugs
>    KVM: selftests: Remove __NR_userfaultfd syscall fallback
> 
>   arch/arm/kernel/signal.c                      |   1 -
>   arch/arm64/kernel/signal.c                    |   1 -
>   arch/csky/kernel/signal.c                     |   4 +-
>   arch/mips/kernel/signal.c                     |   4 +-
>   arch/powerpc/kernel/signal.c                  |   4 +-
>   arch/s390/kernel/signal.c                     |   1 -
>   include/linux/tracehook.h                     |   2 +
>   kernel/entry/common.c                         |   4 +-
>   kernel/rseq.c                                 |   4 +-
>   .../x86/include/{ => uapi}/asm/unistd_32.h    |   0
>   .../x86/include/{ => uapi}/asm/unistd_64.h    |   3 -
>   tools/testing/selftests/kvm/.gitignore        |   1 +
>   tools/testing/selftests/kvm/Makefile          |   3 +
>   tools/testing/selftests/kvm/rseq_test.c       | 131 ++++++++++++++++++
>   14 files changed, 143 insertions(+), 20 deletions(-)
>   rename tools/arch/x86/include/{ => uapi}/asm/unistd_32.h (100%)
>   rename tools/arch/x86/include/{ => uapi}/asm/unistd_64.h (83%)
>   create mode 100644 tools/testing/selftests/kvm/rseq_test.c
> 

Queued v3, thanks.  I'll send it in a separate pull request to Linus 
since it touches stuff outside my usual turf.

Thanks,

Paolo