On 04.11.19 12:25, David Hildenbrand wrote:
> On 24.10.19 13:40, Janosch Frank wrote:
>> Guest registers for protected guests are stored at offset 0x380.
>>
>> Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
>> ---
>> arch/s390/include/asm/kvm_host.h | 4 +++-
>> arch/s390/kvm/kvm-s390.c | 11 +++++++++++
>> 2 files changed, 14 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
>> index 0ab309b7bf4c..5deabf9734d9 100644
>> --- a/arch/s390/include/asm/kvm_host.h
>> +++ b/arch/s390/include/asm/kvm_host.h
>> @@ -336,7 +336,9 @@ struct kvm_s390_itdb {
>> struct sie_page {
>> struct kvm_s390_sie_block sie_block;
>> struct mcck_volatile_info mcck_info; /* 0x0200 */
>> - __u8 reserved218[1000]; /* 0x0218 */
>> + __u8 reserved218[360]; /* 0x0218 */
>> + __u64 pv_grregs[16]; /* 0x380 */
>> + __u8 reserved400[512];
>> struct kvm_s390_itdb itdb; /* 0x0600 */
>> __u8 reserved700[2304]; /* 0x0700 */
>> };
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index 490fde080107..97d3a81e5074 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -3965,6 +3965,7 @@ static int vcpu_post_run(struct kvm_vcpu *vcpu, int exit_reason)
>> static int __vcpu_run(struct kvm_vcpu *vcpu)
>> {
>> int rc, exit_reason;
>> + struct sie_page *sie_page = (struct sie_page *)vcpu->arch.sie_block;
>> /*
>> * We try to hold kvm->srcu during most of vcpu_run (except when run-
>> @@ -3986,8 +3987,18 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
>> guest_enter_irqoff();
>> __disable_cpu_timer_accounting(vcpu);
>> local_irq_enable();
>> + if (kvm_s390_pv_is_protected(vcpu->kvm)) {
>> + memcpy(sie_page->pv_grregs,
>> + vcpu->run->s.regs.gprs,
>> + sizeof(sie_page->pv_grregs));
>> + }
>> exit_reason = sie64a(vcpu->arch.sie_block,
>> vcpu->run->s.regs.gprs);
>> + if (kvm_s390_pv_is_protected(vcpu->kvm)) {
>> + memcpy(vcpu->run->s.regs.gprs,
>> + sie_page->pv_grregs,
>> + sizeof(sie_page->pv_grregs));
>> + }
>
> sie64a will load/save gprs 0-13 from to vcpu->run->s.regs.gprs.
>
> I would have assume that this is not required for prot virt, because the HW has direct access via the sie block?
Yes, that is correct. The load/save in sie64a is not necessary for pv guests.
>
>
> 1. Would it make sense to have a specialized sie64a() (or a parameter, e.g., if you pass in NULL in r3), that optimizes this loading/saving? Eventually we can also optimize which host registers to save/restore then.
Having 2 kinds of sie64a seems not very nice for just saving a small number of cycles.
>
> 2. Avoid this copying here. We have to store the state to vcpu->run->s.regs.gprs when returning to user space and restore the state when coming from user space.
I like this proposal better than the first one and
>
> Also, we access the GPRS from interception handlers, there we might use wrappers like
>
> kvm_s390_set_gprs()
> kvm_s390_get_gprs()
having register accessors might be useful anyway.
But I would like to defer that to a later point in time to keep the changes in here
minimal?
We can add a "TODO" comment in here so that we do not forget about this
for a future patch. Makes sense?
>
> to route to the right location. There are multiple options to optimize this.
