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

[Eric Auger]

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
> 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") ?
> ---
>  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.
> +	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
> +	/* 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 */
> +	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

Thanks

Eric