Re: [PATCH 2/2] x86/kexec/64: Forbid kexec when running as an SEV-ES guest

[Eric W. Biederman]

Joerg Roedel <joro@xxxxxxxxxx> writes:

> From: Joerg Roedel <jroedel@xxxxxxx>
>
> For now, kexec is not supported when running as an SEV-ES guest. Doing
> so requires additional hypervisor support and special code to hand
> over the CPUs to the new kernel in a safe way.
>
> Until this is implemented, do not support kexec in SEV-ES guests.

I don't understand this.

Fundamentally kexec is about doing things more or less inspite of
what the firmware is doing.

I don't have any idea what a SEV-ES is.  But the normal x86 boot doesn't
do anything special.  Is cross cpu IPI emulation buggy?

If this is a move in your face hypervisor like Xen is sometimes I can
see perhaps needing a little bit of different work during bootup.
Perhaps handing back a cpu on system shutdown and asking for more cpus
on system boot up.

What is the actual problem you are trying to avoid?

And yes for a temporary hack the suggestion of putting code into
machine_kexec_prepare seems much more reasonable so we don't have to
carry special case infrastructure for the forseeable future.

Eric


> Cc: stable@xxxxxxxxxxxxxxx # v5.10+
> Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
> ---
>  arch/x86/kernel/machine_kexec_64.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
> index c078b0d3ab0e..f902cc9cc634 100644
> --- a/arch/x86/kernel/machine_kexec_64.c
> +++ b/arch/x86/kernel/machine_kexec_64.c
> @@ -620,3 +620,11 @@ void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages)
>  	 */
>  	set_memory_encrypted((unsigned long)vaddr, pages);
>  }
> +
> +/*
> + * Kexec is not supported in SEV-ES guests yet
> + */
> +bool arch_kexec_supported(void)
> +{
> +	return !sev_es_active();
> +}