Re: [PATCH for-7.1] target/arm: Don't report Statistical Profiling Extension in ID registers

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

On 8/11/22 06:11, Peter Maydell wrote:
> The newly added neoverse-n1 CPU has ID register values which indicate
> the presence of the Statistical Profiling Extension, because the real
> hardware has this feature.  QEMU's TCG emulation does not yet
> implement SPE, though (not even as a minimal stub implementation), so
> guests will crash if they try to use it because the SPE system
> registers don't exist.
> 
> Force ID_AA64DFR0_EL1.PMSVer to 0 in CPU realize for TCG, so that
> we don't advertise to the guest a feature that doesn't exist.
> 
> (We could alternatively do this by editing the value that
> aarch64_neoverse_n1_initfn() sets for this ID register, but
> suppressing the field in realize means we won't re-introduce this bug
> when we add other CPUs that have SPE in hardware, such as the
> Neoverse-V1.)
> 
> An example of a non-booting guest is current mainline Linux (5.19),
> when booting in EL2 on the virt board (ie with -machine
> virtualization=on).
> 
> Reported-by: Zenghui Yu <yuzenghui@huawei.com>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> I think we missed this earlier because it happens not to be hit if
> you boot the kernel into EL1, only EL2.
> ---
>   target/arm/cpu.c | 11 +++++++++++
>   1 file changed, 11 insertions(+)

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


r~