On 11/5/19 1:01 PM, Christian Borntraeger wrote:
>
>
> 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?
I second all of that :-)
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