Re: [PATCH v2 2/2] arm64/kvm: Fine grain _EL2 system registers list that affect nested virtualization

[Miguel Luis]

Hi Eric,

On 29/09/2023 15:08, Eric Auger wrote:
> Hi Miguel,
> On 9/25/23 18:20, Miguel Luis wrote:
>> Some _EL1 registers got included in the _EL2 ranges, which are not
> if they aren't too many, you may list them as it eases the review

Thanks for bringing it up.

Initially I thought those _EL1 registers would be ESR_EL1, TFSR_EL1 and FAR_EL1,
but as I re-run through the process I cannot confirm the statement anymore.
So that statement is a mistake now?

I took as reference Table D18-2 on page D18-6307 where are listed instruction
encodings for non-debug system register accesses. Having to deal with the
document format is surely not an easy task, so I converted it to text using
pdftotext -layout.

After scraping, the end result is a table of encodings which we're allowed to
sort/grep which may be handy to this when you consider the statement that all
accesses (but the exceptions) to system registers ending in _EL2 should trap.

>> affected by NV. Remove them, fine grain the ranges to exclusively
>> include the _EL2 ones and fold SPSR/ELR _EL2 registers into the
>> existing range.
>>
>> Signed-off-by: Miguel Luis <miguel.luis@xxxxxxxxxx>
> Fixes: d0fc0a2519a6 (" KVM: arm64: nv: Add trap forwarding for HCR_EL2") ?

OK.

>> ---
>>  arch/arm64/kvm/emulate-nested.c | 44 ++++++++++++++++++++++++++++-----
>>  1 file changed, 38 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/arm64/kvm/emulate-nested.c b/arch/arm64/kvm/emulate-nested.c
>> index 9ced1bf0c2b7..f6d0c87803f4 100644
>> --- a/arch/arm64/kvm/emulate-nested.c
>> +++ b/arch/arm64/kvm/emulate-nested.c
>> @@ -649,14 +649,46 @@ static const struct encoding_to_trap_config encoding_to_cgt[] __initconst = {
>>  	SR_TRAP(SYS_APGAKEYHI_EL1,	CGT_HCR_APK),
>>  	/* All _EL2 registers */
>>  	SR_RANGE_TRAP(sys_reg(3, 4, 0, 0, 0),
>> -		      sys_reg(3, 4, 3, 15, 7), CGT_HCR_NV),
>> +		      sys_reg(3, 4, 4, 0, 1), CGT_HCR_NV),
>>  	/* Skip the SP_EL1 encoding... */
>> -	SR_TRAP(SYS_SPSR_EL2,		CGT_HCR_NV),
>> -	SR_TRAP(SYS_ELR_EL2,		CGT_HCR_NV),
>> -	SR_RANGE_TRAP(sys_reg(3, 4, 4, 1, 1),
>> -		      sys_reg(3, 4, 10, 15, 7), CGT_HCR_NV),
> I am not sure I fully understand the sysreg encoding but globally there
> are not so many _EL2 regs trapped with .NV. And I can see holes within
> somes ranges defined above (I searched all "if EL2Enabled() &&
> HCR_EL2.NV == '1' then" in the ARM ARM). Maybe I don't know how to use
> the ARM ARM doc but I feel  difficult to understand if the "holes"
> within the encoding of some ranges are unused or are allocated to some
> other sysregs, which wouldn't be trapped by /NV. I fear range encoding
> may be quite risky.

That's definitely fair and I share the same concerns too.
Having table D18-2 sorted helped defining those ranges although I did not
find the answer to those questions. Perhaps we could query for assumptions
on the desired approach in which such implementation would rely.

>> +	SR_RANGE_TRAP(sys_reg(3, 4, 4, 3, 0),
>> +		      sys_reg(3, 4, 10, 6, 7), CGT_HCR_NV),
>> +	/*
>> +	 * Note that the spec. describes a group of MEC registers
>> +	 * whose access should not trap, therefore skip the following:
>> +	 * MECID_A0_EL2, MECID_A1_EL2, MECID_P0_EL2,
>> +	 * MECID_P1_EL2, MECIDR_EL2, VMECID_A_EL2,
>> +	 * VMECID_P_EL2.
>> +	 */
>>  	SR_RANGE_TRAP(sys_reg(3, 4, 12, 0, 0),
>> -		      sys_reg(3, 4, 14, 15, 7), CGT_HCR_NV),
>> +		      sys_reg(3, 4, 12, 1, 1), CGT_HCR_NV),
>> +	/* ICH_AP0R<m>_EL2 */
>> +	SR_RANGE_TRAP(SYS_ICH_AP0R0_EL2,
>> +		      SYS_ICH_AP0R3_EL2, CGT_HCR_NV),
>> +	/* ICH_AP1R<m>_EL2 */
>> +	SR_RANGE_TRAP(SYS_ICH_AP1R0_EL2,
>> +		      SYS_ICH_AP1R3_EL2, CGT_HCR_NV),
>> +	SR_RANGE_TRAP(sys_reg(3, 4, 12, 9, 5),
>> +		      sys_reg(3, 4, 12, 11, 7), CGT_HCR_NV),
>> +	/* ICH_LR<m>_EL2 */
>> +	SR_RANGE_TRAP(SYS_ICH_LR0_EL2,
>> +		      SYS_ICH_LR7_EL2, CGT_HCR_NV),
>> +	SR_RANGE_TRAP(SYS_ICH_LR8_EL2,
>> +		      SYS_ICH_LR15_EL2, CGT_HCR_NV),
>> +	SR_RANGE_TRAP(sys_reg(3, 4, 13, 0, 1),
>> +		      sys_reg(3, 4, 13, 0, 7), CGT_HCR_NV),
>> +	/* AMEVCNTVOFF0<n>_EL2 */
>> +	SR_RANGE_TRAP(sys_reg(3, 4, 13, 8, 0),
>> +		      sys_reg(3, 4, 13, 8, 7), CGT_HCR_NV),
>> +	SR_RANGE_TRAP(sys_reg(3, 4, 13, 9, 0),
>> +		      sys_reg(3, 4, 13, 9, 7), CGT_HCR_NV),
> I think those 2 above ranges can be merged

Oh, indeed. For both AMEVCNTVOFF0<n>_EL2 and AMEVCNTVOFF1<n>_EL2.

>> +	/* AMEVCNTVOFF1<n>_EL2 */
>> +	SR_RANGE_TRAP(sys_reg(3, 4, 13, 10, 0),
>> +		      sys_reg(3, 4, 13, 10, 7), CGT_HCR_NV),
>> +	SR_RANGE_TRAP(sys_reg(3, 4, 13, 11, 0),
>> +		      sys_reg(3, 4, 13, 11, 7), CGT_HCR_NV),
> /* CNT*_EL2 */

OK.

>> +	SR_RANGE_TRAP(sys_reg(3, 4, 14, 0, 3),
>> +		      sys_reg(3, 4, 14, 5, 2), CGT_HCR_NV),
>>  	/* All _EL02, _EL12 registers */
>>  	SR_RANGE_TRAP(sys_reg(3, 5, 0, 0, 0),
>>  		      sys_reg(3, 5, 10, 15, 7), CGT_HCR_NV),
> not related to your patch but wrt the EL02 the only ones that I
> idenftied beeing trapped by NV using above search are
> 
> CNTP_TVAL_EL02	3	5	14	2	0
> CNTP_CTL_EL02	3	5	14	2	1
> CNTP_CVAL_EL02	3	5	14	2	2
> CNTV_TVAL_EL02	3	5	14	3	0
> CNTV_CTL_EL02	3	5	14	3	1
> CNTV_CVAL_EL02	3	5	14	3	2
> 

That matches my search too. FWIW, below are the _EL12 from my search:

AFSR0_EL12 	3 5 5 1 0
AFSR1_EL12 	3 5 5 1 1
AMAIR_EL12 	3 5 5 3 0
CONTEXTIDR_EL12 3 5 13 0 1
CPACR_EL12 	3 5 1 0 2
ESR_EL12 	3 5 5 2 0
FAR_EL12 	3 5 6 0 0
MAIR_EL12 	3 5 10 2 0
SCTLR2_EL12 	3 5 1 0 3
SCTLR_EL12 	3 5 1 0 0
SMCR_EL12 	3 5 1 2 6
TCR2_EL12 	3 5 2 0 3
TCR_EL12 	3 5 2 0 2
TFSR_EL12 	3 5 5 6 0
TTBR0_EL12 	3 5 2 0 0
TTBR1_EL12 	3 5 2 0 1
VBAR_EL12 	3 5 12 0 0
ZCR_EL12 	3 5 1 2 0
TRFCR_EL12 	3 5 1 2 1
PMSCR_EL12 	3 5 9 9 0
CNTKCTL_EL12 	3 5 14 1 0

Thanks

Miguel

> Thanks
> 
> Eric
>