From: Qais Yousef <qais.yousef@arm.com>
To: James Morse <james.morse@arm.com>
Cc: Marc Zyngier <maz@kernel.org>,
linux-arch@vger.kernel.org, Will Deacon <will@kernel.org>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Morten Rasmussen <morten.rasmussen@arm.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC PATCH 1/3] arm64: kvm: Handle Asymmetric AArch32 systems
Date: Tue, 13 Oct 2020 12:59:53 +0100 [thread overview]
Message-ID: <20201013115953.gepxn5dbzrk6x6ec@e107158-lin> (raw)
In-Reply-To: <13eb5d05-9eaf-7640-cd44-cfd7f8820257@arm.com>
On 10/13/20 12:51, James Morse wrote:
> Hi Marc,
>
> On 13/10/2020 11:32, Marc Zyngier wrote:
> > On 2020-10-12 16:32, James Morse wrote:
> >> On 09/10/2020 13:48, Qais Yousef wrote:
> >>> On 10/09/20 13:34, Marc Zyngier wrote:
> >>>> You can try setting vcpu->arch.target to -1, which is already caught by
> >>>> kvm_vcpu_initialized() right at the top of this function. This will
> >>
> >>>> prevent any reentry unless the VMM issues a KVM_ARM_VCPU_INIT ioctl.
> >>
> >> This doesn't reset SPSR, so this lets the VMM restart the guest with a
> >> bad value.
> >
> > That's not my reading of the code. Without a valid target, you cannot enter
> > the guest (kvm_vcpu_initialized() prevents you to do so). To set the target,
> > you need to issue a KVM_ARM_VCPU_INIT ioctl, which eventually calls
>
> > kvm_reset_vcpu(), which does set PSTATE to something legal.
>
> aha! So it does, this is what I was missing.
>
>
> > Or do you mean the guest's SPSR_EL1? Why would that matter?
> >
> >> I think we should make it impossible to return to aarch32 from EL2 on
> >> these systems.
> >
> > And I'm saying that the above fulfills that requirement. Am I missing
> > something obvious?
>
> Nope, I was.
>
> I agree the check on entry from user-space isn't needed.
Thanks both.
So using the vcpu->arch.target = -1 is the best way forward. In my experiments
when I did that I considered calling kvm_reset_vcpu() too, does it make sense
to force the reset here too? Or too heavy handed?
Thanks
--
Qais Yousef
next prev parent reply other threads:[~2020-10-13 12:00 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-08 18:16 [RFC PATCH 0/3] Add support for Asymmetric AArch32 systems Qais Yousef
2020-10-08 18:16 ` [RFC PATCH 1/3] arm64: kvm: Handle " Qais Yousef
2020-10-09 8:12 ` Marc Zyngier
2020-10-09 9:58 ` Qais Yousef
2020-10-09 12:34 ` Marc Zyngier
2020-10-09 12:48 ` Qais Yousef
2020-10-12 15:32 ` James Morse
2020-10-13 10:32 ` Marc Zyngier
2020-10-13 11:51 ` James Morse
2020-10-13 11:59 ` Qais Yousef [this message]
2020-10-13 12:09 ` Marc Zyngier
2020-10-13 12:16 ` Qais Yousef
2020-10-08 18:16 ` [RFC PATCH 2/3] arm64: Add support for asymmetric AArch32 EL0 configurations Qais Yousef
2020-10-08 18:22 ` Randy Dunlap
2020-10-12 10:22 ` Qais Yousef
2020-10-09 6:13 ` Greg Kroah-Hartman
2020-10-09 8:40 ` Will Deacon
2020-10-09 8:50 ` Catalin Marinas
2020-10-09 9:39 ` Catalin Marinas
2020-10-12 12:46 ` Qais Yousef
2020-10-08 18:16 ` [RFC PATCH 3/3] arm64: Handle AArch32 tasks running on non AArch32 cpu Qais Yousef
2020-10-09 7:29 ` Peter Zijlstra
2020-10-09 8:13 ` Morten Rasmussen
2020-10-09 8:31 ` Will Deacon
2020-10-09 8:50 ` Morten Rasmussen
2020-10-09 9:33 ` Catalin Marinas
2020-10-09 9:42 ` Greg Kroah-Hartman
2020-10-09 11:31 ` Qais Yousef
2020-10-09 12:40 ` Catalin Marinas
2020-10-13 14:23 ` Qais Yousef
2020-10-09 9:25 ` Peter Zijlstra
2020-10-09 9:39 ` Qais Yousef
2020-10-09 9:51 ` Catalin Marinas
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