Re: [PATCH] hw/intc/arm_gicv5: Make IRS_IDR0 reads return actual value, not 0

[Jim MacArthur <jim.macarthur@linaro.org>]

On Thu, Oct 08, 2026 at 10:23:27AM +0100, Peter Maydell wrote:
> IN the code for handling reads of IRS_IDR0, we carefully construct
> the correct value starting with cs->irs_idr0 and adjusting it.
> However, we never actually write the final value into *data, so
> the guest will always see zero.
> 
> We didn't notice this before, because Linux happens to not care
> about this register value except to check for the presence of
> virtualization.
> 
> Cc: qemu-stable@nongnu.org
> Fixes: 405ad2e76f13254 ("hw/intc/arm_gicv5: Implement IRS ID regs")
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  hw/intc/arm_gicv5.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/hw/intc/arm_gicv5.c b/hw/intc/arm_gicv5.c
> index 08878193dfc..ebfb0878af3 100644
> --- a/hw/intc/arm_gicv5.c
> +++ b/hw/intc/arm_gicv5.c
> @@ -1433,6 +1433,7 @@ static bool config_readl(GICv5 *s, GICv5Domain domain, hwaddr offset,
>              /* ...which means VIRT_ONE_N is also RES0 */
>              v &= ~R_IRS_IDR0_VIRT_ONE_N_MASK;
>          }
> +        *data = v;
>          return true;
>  
>      case A_IRS_IDR1:

Reviewed-by: Jim MacArthur <jim.macarthur@linaro.org>