Re: [PATCH 1/2] hw/arm/boot: Set SME and SVE EL3 vector lengths when booting kernel

[Richard Henderson <richard.henderson@linaro.org>]

On 10/28/22 00:02, Peter Maydell wrote:
> When we direct boot a kernel on a CPU which emulates EL3, we need
> to set up the EL3 system registers as the Linux kernel documentation
> specifies:
>   https://www.kernel.org/doc/Documentation/arm64/booting.rst
> 
> For SVE and SME this includes:
>      - ZCR_EL3.LEN must be initialised to the same value for all CPUs the
>        kernel is executed on.
>      - SMCR_EL3.LEN must be initialised to the same value for all CPUs the
>        kernel will execute on.
> 
> Although we are technically compliant with this, the "same value" we
> currently use by default is the reset value of 0.  This will end up
> forcing the guest kernel's SVE and SME vector length to be only the
> smallest supported length.
> 
> Initialize the vector length fields to their maximum possible value,
> which is 0xf. If the implementation doesn't actually support that
> vector length then the effective vector length will be constrained
> down to the maximum supported value at point of use.
> 
> This allows the guest to use all the vector lengths the emulated CPU
> supports (by programming the _EL2 and _EL1 versions of these
> registers.)
> 
> Signed-off-by: Peter Maydell<peter.maydell@linaro.org>
> ---
>   hw/arm/boot.c | 2 ++
>   1 file changed, 2 insertions(+)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~