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

Tom Lendacky
2020-04-14T20:15:25Z

On 4/14/20 2:03 PM, Mike Stunes wrote:
> On Mar 19, 2020, at 2:13 AM, Joerg Roedel <joro@8bytes.org> wrote:
>>
>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>
>> The runtime handler needs a GHCB per CPU. Set them up and map them
>> unencrypted.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>> Signed-off-by: Joerg Roedel <jroedel@suse.de>
>> ---
>> 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

>