From: Qais Yousef <qais.yousef@arm.com>
To: Marc Zyngier <maz@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
James Morse <james.morse@arm.com>,
linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org
Subject: Re: [RFC PATCH v2 1/4] arm64: kvm: Handle Asymmetric AArch32 systems
Date: Wed, 21 Oct 2020 15:38:14 +0100 [thread overview]
Message-ID: <20201021143814.vpad2dfg7gplvghy@e107158-lin> (raw)
In-Reply-To: <87587dbfb7bee53eca4d1b837fd8194a@kernel.org>
On 10/21/20 14:51, Marc Zyngier wrote:
> On 2020-10-21 14:35, Qais Yousef wrote:
> > On 10/21/20 13:02, Marc Zyngier wrote:
> > > On 2020-10-21 11:46, Qais Yousef wrote:
> > > > On a system without uniform support for AArch32 at EL0, it is possible
> > > > for the guest to force run AArch32 at EL0 and potentially cause an
> > > > illegal exception if running on the wrong core.
> > >
> > > s/the wrong core/a core without AArch32/
> > >
> > > >
> > > > Add an extra check to catch if the guest ever does that and prevent it
> > >
> > > Not "if the guest ever does that". Rather "let's hope we are lucky
> > > enough
> > > to catch the guest doing that".
> > >
> > > > from running again by resetting vcpu->arch.target and return
> > > > ARM_EXCEPTION_IL.
> > > >
> > > > We try to catch this misbehavior as early as possible and not rely on
> > > > PSTATE.IL to occur.
> > > >
> > > > Tested on Juno by instrumenting the host to:
> > > >
> > > > * Fake asym aarch32.
> > > > * Instrument KVM to make the asymmetry visible to the guest.
> > > >
> > > > Any attempt to run 32bit app in the guest will produce such error on
> > > > qemu:
> > >
> > > Not *any* attempt. Only the ones where the guest exits whilst in
> > > AArch32 EL0. It is perfectly possible for the guest to use AArch32
> > > undetected for quite a while.
> >
> > Thanks Marc! I'll change them all.
> >
> > > >
> > > > # ./test
> > > > error: kvm run failed Invalid argument
> > > > PC=ffff800010945080 X00=ffff800016a45014 X01=ffff800010945058
> > > > X02=ffff800016917190 X03=0000000000000000 X04=0000000000000000
> > > > X05=00000000fffffffb X06=0000000000000000 X07=ffff80001000bab0
> > > > X08=0000000000000000 X09=0000000092ec5193 X10=0000000000000000
> > > > X11=ffff80001608ff40 X12=ffff000075fcde86 X13=ffff000075fcde88
> > > > X14=ffffffffffffffff X15=ffff00007b2105a8 X16=ffff00007b006d50
> > > > X17=0000000000000000 X18=0000000000000000 X19=ffff00007a82b000
> > > > X20=0000000000000000 X21=ffff800015ccd158 X22=ffff00007a82b040
> > > > X23=ffff00007a82b008 X24=0000000000000000 X25=ffff800015d169b0
> > > > X26=ffff8000126d05bc X27=0000000000000000 X28=0000000000000000
> > > > X29=ffff80001000ba90 X30=ffff80001093f3dc SP=ffff80001000ba90
> > > > PSTATE=60000005 -ZC- EL1h
> > > > qemu-system-aarch64: Failed to get KVM_REG_ARM_TIMER_CNT
> > >
> > > It'd be worth working out:
> > > - why does this show an AArch64 mode it we caught the vcpu in AArch32?
> > > - why does QEMU shout about the timer register?
> >
> > /me puts a monocular on
> >
> > Which bit is the AArch64?
>
> It clearly spits out "EL1h", and PSTATE.M is 5, also consistent with EL1h.
>
> > It did surprise me that it is shouting about the timer. My guess was
> > that
> > a timer interrupt at the guest between exit/reentry caused the state
> > change and
> > the failure to read the timer register? Since the target is no longer
> > valid it
> > falls over, hopefully as expected. I could have been naive of course.
> > That
> > explanation made sense to my mind so I didn't dig further.
>
> Userspace is never involved with the timer interrupt, unless you've elected
> to have the interrupt controller in userspace, which I seriously doubt.
>
> As we are introducing a change to the userspace ABI, it'd be interesting
> to find out what is happening here.
Sure. Let me educate myself more about this and find a way to interrogate qemu
and KVM.
Thanks
--
Qais Yousef
next prev parent reply other threads:[~2020-10-21 14:38 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-21 10:46 [RFC PATCH v2 0/4] Add support for Asymmetric AArch32 systems Qais Yousef
2020-10-21 10:46 ` [RFC PATCH v2 1/4] arm64: kvm: Handle " Qais Yousef
2020-10-21 12:02 ` Marc Zyngier
2020-10-21 13:35 ` Qais Yousef
2020-10-21 13:51 ` Marc Zyngier
2020-10-21 14:38 ` Qais Yousef [this message]
2020-11-02 17:58 ` Qais Yousef
2020-10-21 10:46 ` [RFC PATCH v2 2/4] arm64: Add support for asymmetric AArch32 EL0 configurations Qais Yousef
2020-10-21 15:39 ` Will Deacon
2020-10-21 16:21 ` Qais Yousef
2020-10-21 16:52 ` Catalin Marinas
2020-10-21 17:39 ` Will Deacon
2020-10-22 9:53 ` Catalin Marinas
2020-10-21 10:46 ` [RFC PATCH v2 3/4] arm64: export emulate_sys_reg() Qais Yousef
2020-10-21 10:46 ` [RFC PATCH v2 4/4] arm64: Export id_aar64fpr0 via sysfs Qais Yousef
2020-10-21 11:09 ` Marc Zyngier
2020-10-21 11:25 ` Greg Kroah-Hartman
2020-10-21 11:46 ` Marc Zyngier
2020-10-21 12:11 ` Greg Kroah-Hartman
2020-10-21 13:18 ` Qais Yousef
2020-10-21 12:15 ` Catalin Marinas
2020-10-21 13:20 ` Qais Yousef
2020-10-21 13:33 ` Morten Rasmussen
2020-10-21 14:09 ` Catalin Marinas
2020-10-21 14:41 ` Morten Rasmussen
2020-10-21 14:45 ` Will Deacon
2020-10-21 15:10 ` Catalin Marinas
2020-10-21 15:37 ` Will Deacon
2020-10-21 16:18 ` Catalin Marinas
2020-10-21 17:19 ` Will Deacon
2020-10-22 9:55 ` Morten Rasmussen
2020-10-21 14:31 ` Qais Yousef
2020-10-22 10:16 ` Morten Rasmussen
2020-10-22 10:48 ` Qais Yousef
2020-10-21 14:41 ` Will Deacon
2020-10-21 15:03 ` Qais Yousef
2020-10-21 15:23 ` Will Deacon
2020-10-21 16:07 ` Qais Yousef
2020-10-21 17:23 ` Will Deacon
2020-10-21 19:57 ` Qais Yousef
2020-10-21 20:26 ` Will Deacon
2020-10-22 8:16 ` Catalin Marinas
2020-10-22 9:58 ` Qais Yousef
2020-10-22 13:47 ` Qais Yousef
2020-10-22 13:55 ` Greg Kroah-Hartman
2020-10-22 14:31 ` Catalin Marinas
2020-10-22 14:34 ` Qais Yousef
2020-10-26 19:02 ` Qais Yousef
2020-10-26 19:08 ` Greg Kroah-Hartman
2020-10-26 19:18 ` Qais Yousef
2020-10-21 11:28 ` Greg Kroah-Hartman
2020-10-21 13:22 ` Qais Yousef
2020-10-21 11:26 ` [RFC PATCH v2 0/4] Add support for Asymmetric AArch32 systems Greg Kroah-Hartman
2020-10-21 13:15 ` Qais Yousef
2020-10-21 13:31 ` Greg Kroah-Hartman
2020-10-21 13:55 ` Qais Yousef
2020-10-21 14:35 ` Catalin Marinas
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