Re: [RFC 19/37] KVM: s390: protvirt: Add new gprs location handling

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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?


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.

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.

Also, we access the GPRS from interception handlers, there we might use wrappers like

kvm_s390_set_gprs()
kvm_s390_get_gprs()

to route to the right location. There are multiple options to optimize this.

--

Thanks,

David / dhildenb





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