Re: [PATCH] KVM: arm64: add esr_el2 and far_el2 to sysreg

[gengdongjiu]

Hi Marc,
  As James's suggestion, I move injection SEA Error logic to the user space(Qemu), Qemu sets the related guest OS esr/elr/pstate/spsr
through IOCTL KVM_SET_ONE_REG. For the SEA, when Qemu sets the esr_el1.IL bit, it needs to refer to esr_el2.IL, else Qemu does not know the trapped
instruction was a 16-bit or a 32-bit instruction, also it needs to set far_el1 using far_el2, because this is synchronization abort.




On 2017/8/7 23:57, Marc Zyngier wrote:
> +James, since he deals with all things RAS. Please keep him on CC at all
> times.
> 
> On 07/08/17 17:08, Dongjiu Geng wrote:
>> For the firmware-first RAS solution, SEA and SEI is injected
>> by the user space, user space needs to know the esr_el2 and
>> far_el2's value, so add them to sysreg. user space uses
>> the IOCTL KVM_GET_ONE_REG can get their value.
> 
> No.
> 
> This has zero purpose being exposed to userspace. Userspace sees a VM
> that runs at EL1, and nothing else, so exposing EL2 registers doesn't
> make *any* sense.
> 
> If you want something to be exposed to userspace, it has to be properly
> abstracted and describe something that is relevant to the VM. An EL2
> register satisfies none of these conditions.
> 
>>
>> Signed-off-by: Dongjiu Geng <gengdongjiu@xxxxxxxxxx>
>> Signed-off-by: Quanming Wu <wuquanming@xxxxxxxxxx>
>> ---
>>  arch/arm64/include/asm/kvm_host.h | 6 ++++--
>>  arch/arm64/kvm/sys_regs.c         | 6 ++++++
>>  2 files changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
>> index b6242fb..6063eec 100644
>> --- a/arch/arm64/include/asm/kvm_host.h
>> +++ b/arch/arm64/include/asm/kvm_host.h
>> @@ -103,10 +103,12 @@ enum vcpu_sysreg {
>>  	TTBR0_EL1,	/* Translation Table Base Register 0 */
>>  	TTBR1_EL1,	/* Translation Table Base Register 1 */
>>  	TCR_EL1,	/* Translation Control Register */
>> -	ESR_EL1,	/* Exception Syndrome Register */
>> +	ESR_EL1,	/* Exception Syndrome Register for EL1 */
>> +	ESR_EL2,	/* Exception Syndrome Register for EL2 */
>>  	AFSR0_EL1,	/* Auxiliary Fault Status Register 0 */
>>  	AFSR1_EL1,	/* Auxiliary Fault Status Register 1 */
>> -	FAR_EL1,	/* Fault Address Register */
>> +	FAR_EL1,	/* Fault Address Register for EL1 */
>> +	FAR_EL2,	/* Fault Address Register for EL2 */
>>  	MAIR_EL1,	/* Memory Attribute Indirection Register */
>>  	VBAR_EL1,	/* Vector Base Address Register */
>>  	CONTEXTIDR_EL1,	/* Context ID Register */
>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>> index 0e26f8c..0c286bf 100644
>> --- a/arch/arm64/kvm/sys_regs.c
>> +++ b/arch/arm64/kvm/sys_regs.c
>> @@ -987,9 +987,15 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>>  	/* ESR_EL1 */
>>  	{ Op0(0b11), Op1(0b000), CRn(0b0101), CRm(0b0010), Op2(0b000),
>>  	  access_vm_reg, reset_unknown, ESR_EL1 },
>> +	/* ESR_EL2 */
>> +	{ Op0(0b11), Op1(0b100), CRn(0b0101), CRm(0b0010), Op2(0b000),
>> +	  access_vm_reg, reset_unknown, ESR_EL2 },
>>  	/* FAR_EL1 */
>>  	{ Op0(0b11), Op1(0b000), CRn(0b0110), CRm(0b0000), Op2(0b000),
>>  	  access_vm_reg, reset_unknown, FAR_EL1 },
>> +	/* FAR_EL2 */
>> +	{ Op0(0b11), Op1(0b100), CRn(0b0110), CRm(0b0000), Op2(0b000),
>> +	  access_vm_reg, reset_unknown, FAR_EL2 },
>>  	/* PAR_EL1 */
>>  	{ Op0(0b11), Op1(0b000), CRn(0b0111), CRm(0b0100), Op2(0b000),
>>  	  NULL, reset_unknown, PAR_EL1 },
>>
> 
> Also, what do you return here? All you're doing to return to userspace
> is 0x1de7ec7edbadc0deULL (which perfectly matches this patch).
> 
> So for all intents and purposes, this patch is pretty useless.
> 
> Thanks,
> 
> 	M.
>