Re: [PATCH v6 15/21] KVM: ARM64: Add reset and access handlers for PMUSERENR register

[Shannon Zhao <zhaoshenglong@huawei.com>]

On 2015/12/9 1:03, Marc Zyngier wrote:
> On 08/12/15 12:47, Shannon Zhao wrote:
>> > From: Shannon Zhao <shannon.zhao@linaro.org>
>> > 
>> > The reset value of PMUSERENR_EL0 is UNKNOWN, use reset_unknown.
>> > 
>> > Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
>> > ---
>> >  arch/arm64/kvm/sys_regs.c | 5 +++--
>> >  1 file changed, 3 insertions(+), 2 deletions(-)
>> > 
>> > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>> > index c830fde..80b66c0 100644
>> > --- a/arch/arm64/kvm/sys_regs.c
>> > +++ b/arch/arm64/kvm/sys_regs.c
>> > @@ -880,7 +880,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>> >  	  access_pmu_pmxevcntr },
>> >  	/* PMUSERENR_EL0 */
>> >  	{ Op0(0b11), Op1(0b011), CRn(0b1001), CRm(0b1110), Op2(0b000),
>> > -	  trap_raz_wi },
>> > +	  access_pmu_regs, reset_unknown, PMUSERENR_EL0 },
> So while the 64bit view of the register resets as unknown, a CPU
> resetting in 32bit mode resets as 0. I suggest you reset it as zero, and
> document that choice. You may have to revisit all the other registers
> that do reset as unknown for 64bit as well.
> 
Sure.

BTW, here I didn't handle the bits of PMUSERENR which are used to
permit/forbid accessing some PMU registers from EL0. Does it need to add
the handler? Is there any way to get the exceptional level of the
accessing in hypervisor?

Thanks,
-- 
Shannon