KVM: Return ERR_SIGPENDING from hva_to_pfn() if GUP returns -EGAIN

Treat an -EAGAIN return from GUP the same as -EINTR and immediately report
to the caller that a signal is pending.  GUP only returns -EAGAIN if
the _initial_ mmap_read_lock_killable() fails, which in turn onnly fails
if a signal is pending

Note, rwsem_down_read_slowpath() actually returns -EINTR, so GUP is really
just making life harder than it needs to be.  And the call to
mmap_read_lock_killable() in the retry path returns its -errno verbatim,
i.e. GUP (and thus KVM) is already handling locking failure this way, but
only some of the time.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20241010182427.1434605-15-seanjc@google.com>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index c60b542c7241bc168183968db867353c3e51f94c..88db55f9a8b613a828b1a3b7d344ccb14bf50b51 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2946,7 +2946,7 @@ kvm_pfn_t hva_to_pfn(unsigned long addr, bool interruptible, bool *async,
                                 writable, &pfn);
        if (npages == 1)
                return pfn;
-       if (npages == -EINTR)
+       if (npages == -EINTR || npages == -EAGAIN)
                return KVM_PFN_ERR_SIGPENDING;
 
        mmap_read_lock(current->mm);