From: Thomas Gleixner <tglx@linutronix.de>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>,
RT <linux-rt-users@vger.kernel.org>,
maz@kernel.org
Subject: Re: arm64: kvm + RT
Date: Wed, 06 Oct 2021 02:05:14 +0200 [thread overview]
Message-ID: <87v92bdnlx.ffs@tglx> (raw)
In-Reply-To: <20211005105449.GC1664@C02TD0UTHF1T.local>
On Tue, Oct 05 2021 at 11:54, Mark Rutland wrote:
> On Tue, Oct 05, 2021 at 11:52:52AM +0200, Thomas Gleixner wrote:
>> Jan,
>>
>> On Mon, Oct 04 2021 at 19:54, Jan Kiszka wrote:
>> > what's the state of getting kvm working (again?) along RT? Seems
>> > HAVE_POSIX_CPU_TIMERS_TASK_WORK is in conflict with KVM but a
>> > precondition for RT on recent kernels. What's the story behind that?
>>
>> the ARM64 KVM implementation is incorrect vs. TIF handling before
>> VMENTER which breaks the posix cpu timers task work assumptions and also
>> violates a few other expectations. AFAICT the arm64 folks are working on
>> that, but you have to ask them directly what the state of this is.
>
> I think that was dealt with as of mainline commits:
>
> * e1c6b9e1669e44fb ("entry: KVM: Allow use of generic KVM entry w/o full generic support")
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e1c6b9e1669e44fb7f9688e34e460b759e3b9187
>
> * 6caa5812e2d126a0 ("KVM: arm64: Use generic KVM xfer to guest work function")
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6caa5812e2d126a0aa8a17816c1ba6f0a0c2b309
>
> ... unless I'm missing something.
Just a minor detail:
$ cd linus
$ git grep HAVE_POSIX_CPU_TIMERS_TASK_WORK
arch/x86/Kconfig: select HAVE_POSIX_CPU_TIMERS_TASK_WORK
kernel/time/Kconfig:config HAVE_POSIX_CPU_TIMERS_TASK_WORK
kernel/time/Kconfig: default y if POSIX_TIMERS && HAVE_POSIX_CPU_TIMERS_TASK_WORK
$cd rt
$ git grep HAVE_POSIX_CPU_TIMERS_TASK_WORK
arch/arm/Kconfig: select ARCH_SUPPORTS_RT if HAVE_POSIX_CPU_TIMERS_TASK_WORK
arch/arm/Kconfig: select HAVE_POSIX_CPU_TIMERS_TASK_WORK if !KVM
arch/arm64/Kconfig: select ARCH_SUPPORTS_RT if HAVE_POSIX_CPU_TIMERS_TASK_WORK
arch/arm64/Kconfig: select HAVE_POSIX_CPU_TIMERS_TASK_WORK if !KVM
arch/powerpc/Kconfig: select ARCH_SUPPORTS_RT if HAVE_POSIX_CPU_TIMERS_TASK_WORK
arch/powerpc/Kconfig: select HAVE_POSIX_CPU_TIMERS_TASK_WORK if !KVM
arch/x86/Kconfig: select HAVE_POSIX_CPU_TIMERS_TASK_WORK
Which is simply because arm64 does not yet have:
arch/arm64/Kconfig: select HAVE_POSIX_CPU_TIMERS_TASK_WORK
set in mainline to indicate that it does support it unconditionally
including in KVM.
See?
Thanks,
tglx
prev parent reply other threads:[~2021-10-06 0:05 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-04 17:54 arm64: kvm + RT Jan Kiszka
2021-10-05 9:52 ` Thomas Gleixner
2021-10-05 10:01 ` Jan Kiszka
2021-10-05 10:54 ` Mark Rutland
2021-10-06 0:05 ` Thomas Gleixner [this message]
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