Re: [PATCH] xen/arm: Document the erratum #853709 related to Cortex A72

[Julien Grall <julien@xxxxxxx>]

Hi Michal,

On 14/10/2020 11:05, Michal Orzel wrote:
> Workaround for Cortex-A57 erratum #852523 is already
> in Xen but Cortex-A72 erratum #853709 is not although
> it applies to the same issue.
This commit message is a bit confusing because it implies that Xen 
doesn't workaround #852523. However, we do workaround it (there is no 
runtime check) but not document it.
So how about the following commit message?

"The Cortex-A72 erratum #853709 is the same as the Cortex-A57 erratum 
#852523. As the latter is already workaround, we only need to update the 
documentation."
> Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
Other than the commit message, I have cross-checked with the 
documentation ([1]):
Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>

I can update the commit message on commit.

Cheers,

> ---
>   docs/misc/arm/silicon-errata.txt | 1 +
>   xen/arch/arm/domain.c            | 6 ++++--
>   2 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/docs/misc/arm/silicon-errata.txt b/docs/misc/arm/silicon-errata.txt
> index e15d0923e9..1f18a9df58 100644
> --- a/docs/misc/arm/silicon-errata.txt
> +++ b/docs/misc/arm/silicon-errata.txt
> @@ -50,6 +50,7 @@ stable hypervisors.
>   | ARM            | Cortex-A57      | #834220         | ARM64_ERRATUM_834220   
>  |
>   | ARM            | Cortex-A57      | #1319537        | N/A                    
>  |
>   | ARM            | Cortex-A72      | #1319367        | N/A                    
>  |
> +| ARM            | Cortex-A72      | #853709         | N/A                     
> |
>   | ARM            | Cortex-A76      | #1165522        | N/A                    
>  |
>   | ARM            | Neoverse-N1     | #1165522        | N/A
>   | ARM            | MMU-500         | #842869         | N/A                    
>  |
> diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
> index 3b37f899b9..18cafcdda7 100644
> --- a/xen/arch/arm/domain.c
> +++ b/xen/arch/arm/domain.c
> @@ -216,7 +216,8 @@ static void ctxt_switch_to(struct vcpu *n)
>       WRITE_SYSREG64(n->arch.ttbr1, TTBR1_EL1);
>   
>       /*
> -     * Erratum #852523: DACR32_EL2 must be restored before one of the
> +     * Erratum #852523 (Cortex-A57) or erratum #853709 (Cortex-A72):
> +     * DACR32_EL2 must be restored before one of the
>        * following sysregs: SCTLR_EL1, TCR_EL1, TTBR0_EL1, TTBR1_EL1 or
>        * CONTEXTIDR_EL1.
>        */
> @@ -245,7 +246,8 @@ static void ctxt_switch_to(struct vcpu *n)
>   
>       /*
>        * This write to sysreg CONTEXTIDR_EL1 ensures we don't hit erratum
> -     * #852523. I.e DACR32_EL2 is not correctly synchronized.
> +     * #852523 (Cortex-A57) or #853709 (Cortex-A72).
> +     * I.e DACR32_EL2 is not correctly synchronized.
>        */
>       WRITE_SYSREG(n->arch.contextidr, CONTEXTIDR_EL1);
>       WRITE_SYSREG(n->arch.tpidr_el0, TPIDR_EL0);
[1] https://developer.arm.com/documentation/epm012079/11/

--
Julien Grall