[PATCH 1/2] KVM: Set up async page faults only for faults that need to wait

[Christian Borntraeger <borntraeger@linux.ibm.com>]

hva_to_pfn() checks a FOLL_NOWAIT gup() for EINTR, EAGAIN and EHWPOISON.
There might be others like -EFAULT for VM_FAULT_SIGBUS.  For those other
errors, reporting KVM_PFN_ERR_NEEDS_IO would be wrong as it triggers an
async_pf resulting in endless retries.

Return KVM_PFN_ERR_NEEDS_IO only if gup() returned 0 pages and report
the error otherwise.

Fixes: 0857b9e95c1a ("KVM: Enable async page fault processing")
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
---
 virt/kvm/kvm_main.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5a782849521c..34b38d7512c3 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3048,6 +3048,7 @@ kvm_pfn_t hva_to_pfn(struct kvm_follow_pfn *kfp)
 			pfn = KVM_PFN_ERR_FAULT;
 	} else {
 		if ((kfp->flags & FOLL_NOWAIT) &&
+		    npages == 0 && /* no PFN_ERR_NEEDS_IO on errors */
 		    vma_is_valid(vma, kfp->flags & FOLL_WRITE))
 			pfn = KVM_PFN_ERR_NEEDS_IO;
 		else
-- 
2.53.0