Re: [PATCH 01/11] KVM: arm64: Store vcpu on the stack during __guest_enter()

James Morse
2017-08-08T16:48:12Z

Hi Christoffer,

On 06/06/17 20:59, Christoffer Dall wrote:
> On Mon, May 15, 2017 at 06:43:49PM +0100, James Morse wrote:
>> KVM uses tpidr_el2 as its private vcpu register, which makes sense for
>> non-vhe world switch as only KVM can access this register. This means
>> vhe Linux has to use tpidr_el1, which KVM has to save/restore as part
>> of the host context.
>>
>> __guest_enter() stores the host_ctxt on the stack, do the same with
>> the vcpu.

>> diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
>> index 12ee62d6d410..113735df7d01 100644
>> --- a/arch/arm64/kvm/hyp/entry.S
>> +++ b/arch/arm64/kvm/hyp/entry.S
>> @@ -159,9 +159,15 @@ abort_guest_exit_end:
>> ENDPROC(__guest_exit)
>>
>> ENTRY(__fpsimd_guest_restore)
>> + // x0: esr
>> + // x1: vcpu
>> + // x2-x29,lr: vcpu regs
>> + // vcpu x0-x1 on the stack
>> stp x2, x3, [sp, #-16]!
>> stp x4, lr, [sp, #-16]!
>>
>> + mov x3, x1
>> +
>
> nit: can you avoid this by using x1 for the vcpu pointer in this routine
> instead?

Unfortunately x1 is clobbered by the __fpsimd_{save,restore}_state() macros that
are called further down this function.

(its a bit obscure:
> fpsimd_save x0, 1
that '1' is used to generate 'x1' or 'w1' in includes/asm/fpsimdmacros.h)

Thanks,

James