In case of a fault retry exit sie64a() with the gmap_fault indication set.
This makes it possbile to handle async page faults without the need for mm notifiers.
Based on a patch from Marin Schwidefsky.
Todo:
- Add access to distinguish fault types to prevent double fault
Signed-off-by: Dominik Dingel <dingel@xxxxxxxxxxxxxxxxxx>
---
arch/s390/include/asm/processor.h | 7 +++++++
arch/s390/kvm/kvm-s390.c | 15 +++++++++++++++
arch/s390/mm/fault.c | 29 +++++++++++++++++++++++++----
arch/s390/mm/pgtable.c | 1 +
4 files changed, 48 insertions(+), 4 deletions(-)
diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h
index 6b49987..938d92c 100644
--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -77,6 +77,13 @@ struct thread_struct {
unsigned long ksp; /* kernel stack pointer */
mm_segment_t mm_segment;
unsigned long gmap_addr; /* address of last gmap fault. */
+#define PFAULT_EN 1
+#define PFAULT_PEND 2
+ unsigned long gmap_pfault; /*
+ * indicator if pfault is enabled for a
+ * guest and if a guest pfault is
+ * pending
+ */
struct per_regs per_user; /* User specified PER registers */
struct per_event per_event; /* Cause of the last PER trap */
unsigned long per_flags; /* Flags to control debug behavior */
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index a44c0dc..c2ae2c4 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -706,6 +706,17 @@ static int kvm_s390_handle_requests(struct kvm_vcpu *vcpu)
return 0;
}
+static void kvm_arch_fault_in_sync(struct kvm_vcpu *vcpu)
+{
+ hva_t fault_addr;
+ /* TODO let current->thread.gmap_pfault indicate read or write fault */
+ struct mm_struct *mm = current->mm;
+ down_read(&mm->mmap_sem);
+ fault_addr = __gmap_fault(current->thread.gmap_addr, vcpu->arch.gmap);
+ get_user_pages(current, mm, fault_addr, 1, 1, 0, NULL, NULL);
+ up_read(&mm->mmap_sem);
+}
+
static int __vcpu_run(struct kvm_vcpu *vcpu)
{
int rc;
@@ -739,6 +750,10 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
if (rc < 0) {
if (kvm_is_ucontrol(vcpu->kvm)) {
rc = SIE_INTERCEPT_UCONTROL;
+ } else if (test_bit(PFAULT_PEND,
+ ¤t->thread.gmap_pfault)) {
+ kvm_arch_fault_in_sync(vcpu);
+ rc = 0;
} else {
VCPU_EVENT(vcpu, 3, "%s", "fault in sie instruction");
trace_kvm_s390_sie_fault(vcpu);
diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index c5cfb6f..61b1644 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -50,6 +50,7 @@
#define VM_FAULT_BADMAP 0x020000
#define VM_FAULT_BADACCESS 0x040000
#define VM_FAULT_SIGNAL 0x080000
+#define VM_FAULT_PFAULT 0x100000
static unsigned long store_indication __read_mostly;
@@ -226,6 +227,7 @@ static noinline void do_fault_error(struct pt_regs *regs, int fault)
return;
}
case VM_FAULT_BADCONTEXT:
+ case VM_FAULT_PFAULT:
do_no_context(regs);
break;
case VM_FAULT_SIGNAL:
@@ -263,6 +265,9 @@ static noinline void do_fault_error(struct pt_regs *regs, int fault)
*/
static inline int do_exception(struct pt_regs *regs, int access)
{
+#ifdef CONFIG_PGSTE
+ struct gmap *gmap;
+#endif
struct task_struct *tsk;
struct mm_struct *mm;
struct vm_area_struct *vma;
@@ -301,9 +306,10 @@ static inline int do_exception(struct pt_regs *regs, int access)
down_read(&mm->mmap_sem);
#ifdef CONFIG_PGSTE
- if ((current->flags & PF_VCPU) && S390_lowcore.gmap) {
- address = __gmap_fault(address,
- (struct gmap *) S390_lowcore.gmap);
+ gmap = (struct gmap *)
+ ((current->flags & PF_VCPU) ? S390_lowcore.gmap : 0);
+ if (gmap) {
+ address = __gmap_fault(address, gmap);
if (address == -EFAULT) {
fault = VM_FAULT_BADMAP;
goto out_up;
@@ -312,6 +318,8 @@ static inline int do_exception(struct pt_regs *regs, int access)
fault = VM_FAULT_OOM;
goto out_up;
}
+ if (test_bit(PFAULT_EN, ¤t->thread.gmap_pfault))
+ flags |= FAULT_FLAG_RETRY_NOWAIT;
}
#endif
@@ -368,9 +376,22 @@ retry:
regs, address);
}
if (fault & VM_FAULT_RETRY) {
+#ifdef CONFIG_PGSTE
+ if (gmap &&
+ test_bit(PFAULT_EN, ¤t->thread.gmap_pfault)) {
+ /* FAULT_FLAG_RETRY_NOWAIT has been set,
+ * mmap_sem has not been released */
+ /* TODO use access to distinguish fault type */
+ set_bit(PFAULT_PEND,
+ ¤t->thread.gmap_pfault);
+ fault = VM_FAULT_PFAULT;
+ goto out_up;
+ }
+#endif
/* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
* of starvation. */
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
+ flags &= ~(FAULT_FLAG_ALLOW_RETRY |
+ FAULT_FLAG_RETRY_NOWAIT);
flags |= FAULT_FLAG_TRIED;
down_read(&mm->mmap_sem);
goto retry;
diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 5fb7f19..14d067d 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -540,6 +540,7 @@ unsigned long __gmap_fault(unsigned long address, struct gmap *gmap)
int rc;
current->thread.gmap_addr = address;
+ clear_bit(PFAULT_PEND, ¤t->thread.gmap_pfault);
segment_ptr = gmap_table_walk(address, gmap);
if (IS_ERR(segment_ptr))
return -EFAULT;
--
1.8.1.6
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