Re: [PATCH] target/arm: Fix CNTPCT_EL0 trapping from EL0 when HCR_EL2.E2H is 0

[Oleksandr Tyshchenko]

On 22.09.23 16:21, Michal Orzel wrote:

Hello Michal


> On an attempt to access CNTPCT_EL0 from EL0 using a guest running on top
> of Xen, a trap from EL2 was observed which is something not reproducible
> on HW (also, Xen does not trap accesses to physical counter).
> 
> This is because gt_counter_access() checks for an incorrect bit (1
> instead of 0) of CNTHCTL_EL2 if HCR_EL2.E2H is 0 and access is made to
> physical counter. Refer ARM ARM DDI 0487J.a, D19.12.2:
> When HCR_EL2.E2H is 0:
>   - EL1PCTEN, bit [0]: refers to physical counter
>   - EL1PCEN, bit [1]: refers to physical timer registers
> 
> Fix it by checking for the right bit (i.e. 0) and update the comment
> referring to incorrect bit name.
> 
> Fixes: 5bc8437136fb ("target/arm: Update timer access for VHE")
> Signed-off-by: Michal Orzel <michal.orzel@amd.com>


You can add my:

[with Zephyr running as Xen guest and accessing CNTPCT_EL0 from EL0 ]

Tested-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>

> ---
> This is now in conformance to ARM ARM CNTPCT_EL0 pseudocode:
> if PSTATE.EL == EL0 then
> ...
>      elif EL2Enabled() && HCR_EL2.E2H == '0' && CNTHCTL_EL2.EL1PCTEN == '0' 
> then
>          AArch64.SystemAccessTrap(EL2, 0x18);
> ---
>   target/arm/helper.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/target/arm/helper.c b/target/arm/helper.c
> index 3b22596eabf3..3a2d77b3f81e 100644
> --- a/target/arm/helper.c
> +++ b/target/arm/helper.c
> @@ -2483,9 +2483,9 @@ static CPAccessResult gt_counter_access(CPUARMState 
> *env, int timeridx,
>                   return CP_ACCESS_TRAP_EL2;
>               }
>           } else {
> -            /* If HCR_EL2.<E2H> == 0: check CNTHCTL_EL2.EL1PCEN. */
> +            /* If HCR_EL2.<E2H> == 0: check CNTHCTL_EL2.EL1PCTEN. */
>               if (has_el2 && timeridx == GTIMER_PHYS &&
> -                !extract32(env->cp15.cnthctl_el2, 1, 1)) {
> +                !extract32(env->cp15.cnthctl_el2, 0, 1)) {
>                   return CP_ACCESS_TRAP_EL2;
>               }
>           }