Re: [PATCH 40/70] x86/sev-es: Setup per-cpu GHCBs for the runtime handler

[Tom Lendacky]

On 4/14/20 2:03 PM, Mike Stunes wrote:
> On Mar 19, 2020, at 2:13 AM, Joerg Roedel <joro@xxxxxxxxxx> wrote:
> > From: Tom Lendacky <thomas.lendacky@xxxxxxx>
> >
> > The runtime handler needs a GHCB per CPU. Set them up and map them
> > unencrypted.
> >
> > Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> > Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
> > ---
> > arch/x86/include/asm/mem_encrypt.h |  2 ++
> > arch/x86/kernel/sev-es.c           | 28 +++++++++++++++++++++++++++-
> > arch/x86/kernel/traps.c            |  3 +++
> > 3 files changed, 32 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
> > index c17980e8db78..4bf5286310a0 100644
> > --- a/arch/x86/kernel/sev-es.c
> > +++ b/arch/x86/kernel/sev-es.c
> > @@ -197,6 +203,26 @@ static bool __init sev_es_setup_ghcb(void)
> > 	return true;
> > }
> >
> > +void sev_es_init_ghcbs(void)
> > +{
> > +	int cpu;
> > +
> > +	if (!sev_es_active())
> > +		return;
> > +
> > +	/* Allocate GHCB pages */
> > +	ghcb_page = __alloc_percpu(sizeof(struct ghcb), PAGE_SIZE);
> > +
> > +	/* Initialize per-cpu GHCB pages */
> > +	for_each_possible_cpu(cpu) {
> > +		struct ghcb *ghcb = (struct ghcb *)per_cpu_ptr(ghcb_page, cpu);
> > +
> > +		set_memory_decrypted((unsigned long)ghcb,
> > +				     sizeof(*ghcb) >> PAGE_SHIFT);
> > +		memset(ghcb, 0, sizeof(*ghcb));
> > +	}
> > +}
> > +
>
> set_memory_decrypted needs to check the return value. I see it
> consistently return ENOMEM. I've traced that back to split_large_page
> in arch/x86/mm/pat/set_memory.c.

At that point the guest won't be able to communicate with the hypervisor, 
too. Maybe we should BUG() here to terminate further processing?

Thanks,
Tom

>