On 11/5/19 2:55 PM, David Hildenbrand wrote:
> On 05.11.19 13:39, Janosch Frank wrote:
>> 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
>
> It was actually an additional proposal :)
>
> 1. avoids unnecessary saving/loading/saving/restoring
> 2. avoids the two memcpy
>
>>>>
>>>> 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?
>
> While it makes sense, I guess one could come up with a patch for 2. in
> less than 30 minutes ... but yeah, whatever you prefer. ;)
>
Just to get it fully right we'd need to:
a. Synchronize registers into/from vcpu run in sync_regs/store_regs
b. Sprinkle get/set_gpr(int nr) over most of the files in arch/s390/kvm
That's your proposal?
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