[PATCH v5 1/2] arm64: kvm: allows kvm cpu hotplug
takahiro.akashi at linaro.org
Mon Oct 12 22:38:09 PDT 2015
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?
> This patch prevents me from running vms on such a platform, qemu gives:
>> kvm : 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 at linaro.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)
>> + hvc #HVC_RESET
>> + ret
>> .macro invalid_vector label, target
>> .align 2
>> @@ -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  - I can't find the details in the archive)
>  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
>> + eret
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