Re: [RFC PATCH 16/16] target/arm/kvm-rme: Disable readonly mappings

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

On 1/27/23 05:07, Jean-Philippe Brucker wrote:
> KVM does not support creating read-only mappings for realms at the
> moment. Add an arch helper to detect whether read-only mappings are
> supported.
> 
> Device ROM and flash normally use read-only mappings. Device ROM seems
> limited to legacy use and does not need to be trusted by the guest, so
> trapping reads should be fine. Flash on the other hand, is used for the
> firmware and needs to be both executable and measured. It may be
> necessary to replace flash with RAM in order to run firmwares like edk2
> in realms.
> 
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> ---
>   include/sysemu/kvm.h | 2 ++
>   accel/kvm/kvm-all.c  | 8 +++++++-
>   target/arm/kvm-rme.c | 9 +++++++++
>   3 files changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
> index e9a97eda8c..8d467c76c6 100644
> --- a/include/sysemu/kvm.h
> +++ b/include/sysemu/kvm.h
> @@ -581,5 +581,7 @@ bool kvm_arch_cpu_check_are_resettable(void);
>   
>   bool kvm_dirty_ring_enabled(void);
>   
> +bool kvm_arch_readonly_mem_allowed(KVMState *s);
> +
>   uint32_t kvm_dirty_ring_size(void);
>   #endif
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index f99b0becd8..56cdd2e9e9 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -2267,6 +2267,11 @@ bool kvm_dirty_ring_enabled(void)
>       return kvm_state->kvm_dirty_ring_size ? true : false;
>   }
>   
> +bool __attribute__((weak)) kvm_arch_readonly_mem_allowed(KVMState *s)
> +{
> +    return true;
> +}

Not a fan of the weak.  Just populate this like kvm_arch_cpu_check_are_resettable.


r~