[PATCH 2/3] KVM: ARM: Let guest instruction mapping fail.

[Rusty Russell <rusty@xxxxxxxxxxxxxxx>]

There is a race (SMP guest and host only) where the instruction we
faulted on is unmapped before we get to reading it.  In this (very
unlikely!) case, we should simply return to the guest.  It will
probably do the right thing next time.

Signed-off-by: Rusty Russell <rusty.russell@xxxxxxxxxx>

diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index 6909a83..89ede94 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -587,11 +587,11 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run)
  * @len:	length to copy
  * @priv:	use guest PL1 (ie. kernel) mappings, otherwise use guest PL0 mappings.
  *
- * Returns 0 on success, or errno.
+ * Returns true on success, false on failure (unlikely, but retry).
  */
-static int copy_from_guest_va(struct kvm_vcpu *vcpu,
-			      void *dest, unsigned long va, size_t len,
-			      bool priv)
+static bool copy_from_guest_va(struct kvm_vcpu *vcpu,
+			       void *dest, unsigned long va, size_t len,
+			       bool priv)
 {
 	u64 par;
 	phys_addr_t pc_ipa;
@@ -602,8 +602,9 @@ static int copy_from_guest_va(struct kvm_vcpu *vcpu,
 	do {
 		par = __kvm_va_to_pa(vcpu, va & PAGE_MASK, priv);
 		if (par & 1) {
-			kvm_err("I/O Abort from invalid instruction address? Wrong!\n");
-			return -EINVAL;
+			kvm_err("I/O Abort from invalid instruction address"
+				" %#lx!\n", va);
+			return false;
 		}
 
 		if (par & (1U << 11)) {
@@ -626,13 +627,13 @@ static int copy_from_guest_va(struct kvm_vcpu *vcpu,
 
 		err = kvm_read_guest(vcpu->kvm, pc_ipa, dest, cur_len);
 		if (unlikely(err))
-			return err;
+			return false;
 
 		len -= cur_len;
 		va += cur_len;
 	} while (unlikely(len != 0));
 
-	return 0;
+	return true;
 }
 
 /**
@@ -649,7 +650,6 @@ static int copy_from_guest_va(struct kvm_vcpu *vcpu,
 static int invalid_io_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa)
 {
 	unsigned long instr;
-	int err;
 
 	if (vcpu->arch.regs.cpsr & PSR_T_BIT) {
 		/* TODO: Check validity of PC IPA and IPA2!!! */
@@ -658,12 +658,10 @@ static int invalid_io_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa)
 		return -EINVAL;
 	}
 
-	err = copy_from_guest_va(vcpu, &instr, vcpu->arch.regs.pc, sizeof(instr),
-				 vcpu_mode_priv(vcpu));
-	if (err) {
-		kvm_err("Could not copy guest instruction\n");
-		return err;
-	}
+	/* If it fails (SMP race?), we reenter guest for it to retry. */
+	if (!copy_from_guest_va(vcpu, &instr, vcpu->arch.regs.pc, sizeof(instr),
+				vcpu_mode_priv(vcpu)))
+		return 1;
 
 	return kvm_emulate_mmio_ls(vcpu, fault_ipa, instr);
 }
_______________________________________________
kvmarm mailing list
kvmarm@xxxxxxxxxxxxxxxxxxxxx
https://lists.cs.columbia.edu/cucslists/listinfo/kvmarm