Re: [PATCH v2 05/21] arm64: KVM: VHE: Turn VTCR_EL2 setup into a reusable macro

From: Marc Zyngier
Date: Mon Feb 01 2016 - 09:22:06 EST


On 01/02/16 13:13, Christoffer Dall wrote:
> On Mon, Jan 25, 2016 at 03:53:39PM +0000, Marc Zyngier wrote:
>> On a VHE-capable system, there is no point in setting VTCR_EL2
>> at KVM init time. We can perfectly set it up when the kernel
>> boots, removing the need for a more complicated configuration.
>
> what's the complicated configuration which is avoided?

With VHE, there is no hyp-init at all, so what we avoid is a weird init
sequence where we have to execute part of this hyp-init, but not all of it.

>>
>> In order to allow this, turn VTCR_EL2 setup into a macro that
>> we'll be able to reuse at boot time.
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
>> ---
>> arch/arm64/include/asm/kvm_mmu.h | 23 +++++++++++++++++++++++
>> arch/arm64/kvm/hyp-init.S | 18 +-----------------
>> 2 files changed, 24 insertions(+), 17 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
>> index 7364339..d3e6d7b 100644
>> --- a/arch/arm64/include/asm/kvm_mmu.h
>> +++ b/arch/arm64/include/asm/kvm_mmu.h
>> @@ -56,6 +56,29 @@
>>
>> #ifdef __ASSEMBLY__
>>
>> +#include <asm/kvm_arm.h>
>> +
>> +.macro setup_vtcr tmp1, tmp2
>> + mov \tmp1, #(VTCR_EL2_FLAGS & 0xffff)
>> + movk \tmp1, #(VTCR_EL2_FLAGS >> 16), lsl #16
>> + /*
>> + * Read the PARange bits from ID_AA64MMFR0_EL1 and set the PS bits in
>> + * VTCR_EL2.
>> + */
>> + mrs \tmp2, id_aa64mmfr0_el1
>> + bfi \tmp1, \tmp2, #16, #3
>> + /*
>> + * Read the VMIDBits bits from ID_AA64MMFR1_EL1 and set the VS bit in
>> + * VTCR_EL2.
>> + */
>> + mrs \tmp2, ID_AA64MMFR1_EL1
>> + ubfx \tmp2, \tmp2, #5, #1
>> + lsl \tmp2, \tmp2, #VTCR_EL2_VS
>> + orr \tmp1, \tmp1, \tmp2
>> +
>> + msr vtcr_el2, \tmp1
>> + isb
>> +.endm
>
> this feels like an awful lot of code in a header file.

interrupt_head.S respectfully disagrees with you ;-).

> Is it crazy to imagine wanting to have different T0SZ for different VMs
> in the future? In that case, the T0SZ stuff should stay in KVM...

That's a rather compelling argument indeed. I'll see if I can turn the
thing around in a slightly nicer way. How about moving it out of
hyp-init.S altogether, and into C code?

Thanks,

M.
--
Jazz is not dead. It just smells funny...