linux-kernel - Re: [PATCH v5 1/2] arm64: kvm: allows kvm cpu hotplug

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Date:	Tue, 13 Oct 2015 14:38:09 +0900
From:	AKASHI Takahiro <takahiro.akashi@...aro.org>
To:	James Morse <james.morse@....com>
Cc:	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Mark Rutland <Mark.Rutland@....com>,
	"christoffer.dall@...aro.org" <christoffer.dall@...aro.org>,
	"geoff@...radead.org" <geoff@...radead.org>,
	"broonie@...nel.org" <broonie@...nel.org>,
	"david.griego@...aro.org" <david.griego@...aro.org>,
	"freddy77@...il.com" <freddy77@...il.com>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 1/2] arm64: kvm: allows kvm cpu hotplug

On 10/12/2015 10:28 PM, James Morse wrote:
> On 29/05/15 06:38, AKASHI Takahiro wrote:
>> The current kvm implementation on arm64 does cpu-specific initialization
>> at system boot, and has no way to gracefully shutdown a core in terms of
>> kvm. This prevents, especially, kexec from rebooting the system on a boot
>> core in EL2.
>>
>> This patch adds a cpu tear-down function and also puts an existing cpu-init
>> code into a separate function, kvm_arch_hardware_disable() and
>> kvm_arch_hardware_enable() respectively.
>> We don't need arm64-specific cpu hotplug hook any more.
>
> I think we do... on platforms where cpuidle uses psci to temporarily turn
> off cores that aren't in use, we lose the el2 state. This hotplug hook
> restores the state, even if there a no vms running.

If I understand you correctly, with or without my patch, kvm doesn't work
  under cpuidle anyway. Right?

If so, saving/restoring cpu states (or at least, kicking cpu hotplug hooks)
is cpuidle driver's responsibility, isn't it?

-Takahiro AKASHI

> This patch prevents me from running vms on such a platform, qemu gives:
>> kvm [1500]: Unsupported exception type: 6264688KVM internal error.
> Suberror: 0
>
> kvmtool goes with a more dramatic:
>> KVM exit reason: 17 ("KVM_EXIT_INTERNAL_ERROR")
>
> Disabling CONFIG_ARM_CPUIDLE solves this problem.
>
>
> (Sorry to revive an old thread - I've been using v4 of this patch for the
> hibernate/suspend-to-disk series).
>
>
>> Since this patch modifies common part of code between arm and arm64, one
>> stub definition, __cpu_reset_hyp_mode(), is added on arm side to avoid
>> compiling errors.
>>
>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@...aro.org>
>
>> diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
>> index fd085ec..afe6263 100644
>> --- a/arch/arm64/kvm/hyp.S
>> +++ b/arch/arm64/kvm/hyp.S
>> @@ -1136,6 +1136,11 @@ ENTRY(kvm_call_hyp)
>>   	ret
>>   ENDPROC(kvm_call_hyp)
>>
>> +ENTRY(kvm_call_reset)
>> +	hvc	#HVC_RESET
>> +	ret
>> +ENDPROC(kvm_call_reset)
>> +
>>   .macro invalid_vector	label, target
>>   	.align	2
>>   \label:
>> @@ -1179,10 +1184,27 @@ el1_sync:					// Guest trapped into EL2
>>   	cmp	x18, #HVC_GET_VECTORS
>>   	b.ne	1f
>>   	mrs	x0, vbar_el2
>> -	b	2f
>> -
>> -1:	/* Default to HVC_CALL_HYP. */
>> +	b	do_eret
>>
>> +	/* jump into trampoline code */
>> +1:	cmp	x18, #HVC_RESET
>> +	b.ne	2f
>> +	/*
>> +	 * Entry point is:
>> +	 *	TRAMPOLINE_VA
>> +	 *	+ (__kvm_hyp_reset - (__hyp_idmap_text_start & PAGE_MASK))
>> +	 */
>> +	adrp	x2, __kvm_hyp_reset
>> +	add	x2, x2, #:lo12:__kvm_hyp_reset
>> +	adrp	x3, __hyp_idmap_text_start
>> +	add	x3, x3, #:lo12:__hyp_idmap_text_start
>> +	and	x3, x3, PAGE_MASK
>> +	sub	x2, x2, x3
>> +	ldr	x3, =TRAMPOLINE_VA
>> +	add	x2, x2, x3
>> +	br	x2				// no return
>> +
>> +2:	/* Default to HVC_CALL_HYP. */
>
> What was the reason not to use kvm_call_hyp(__kvm_hyp_reset, ...)?
> (You mentioned you wanted to at [0] - I can't find the details in the archive)
>
>
> Thanks,
>
> James
>
>
> [0] http://lists.infradead.org/pipermail/kexec/2015-April/335533.html
>
>
>>   	push	lr, xzr
>>
>>   	/*
>> @@ -1196,7 +1218,9 @@ el1_sync:					// Guest trapped into EL2
>>   	blr	lr
>>
>>   	pop	lr, xzr
>> -2:	eret
>> +
>> +do_eret:
>> +	eret
>>
>>   el1_trap:
>>   	/*
>>
>
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