[PATCH 12/12] s390/vfio-ap: Make sure nib is shared

Tony Krowiak
2023-08-15T18:44:59Z

Since the NIB is visible by HW, KVM and the (PV) guest it needs to be
in non-secure or secure but shared storage. Return code 6 is used to
indicate to a PV guest that its NIB would be on secure, unshared
storage and therefore the NIB address is invalid.

Unfortunately we have no easy way to check if a page is unshared after
vfio_pin_pages() since it will automatically export an unshared page
if the UV pin shared call did not succeed due to a page being in
unshared state.

Therefore we use the fact that UV pinning it a second time is a nop
but trying to pin an exported page is an error (0x102). If we
encounter this error, we do a vfio unpin and import the page again,
since vfio_pin_pages() exported it.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
Acked-by: Halil Pasic <pasic@linux.ibm.com>
Tested-by: Viktor Mihajlovski <mihajlov@linux.ibm.com>
---
drivers/s390/crypto/vfio_ap_ops.c | 30 ++++++++++++++++++++++++++++++
1 file changed, 30 insertions(+)

diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index 8bda52c46df0..0509f80622cd 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -359,6 +359,28 @@ static int vfio_ap_validate_nib(struct kvm_vcpu *vcpu, dma_addr_t *nib)
return 0;
}

+static int ensure_nib_shared(unsigned long addr, struct gmap *gmap)
+{
+ int ret;
+
+ /*
+ * The nib has to be located in shared storage since guest and
+ * host access it. vfio_pin_pages() will do a pin shared and
+ * if that fails (possibly because it's not a shared page) it
+ * calls export. We try to do a second pin shared here so that
+ * the UV gives us an error code if we try to pin a non-shared
+ * page.
+ *
+ * If the page is already pinned shared the UV will return a success.
+ */
+ ret = uv_pin_shared(addr);
+ if (ret) {
+ /* vfio_pin_pages() likely exported the page so let's re-import */
+ gmap_convert_to_secure(gmap, addr);
+ }
+ return ret;
+}
+
/**
* vfio_ap_irq_enable - Enable Interruption for a APQN
*
@@ -422,6 +444,14 @@ static struct ap_queue_status vfio_ap_irq_enable(struct vfio_ap_queue *q,
h_nib = page_to_phys(h_page) | (nib & ~PAGE_MASK);
aqic_gisa.gisc = isc;

+ /* NIB in non-shared storage is a rc 6 for PV guests */
+ if (kvm_s390_pv_cpu_is_protected(vcpu) &&
+ ensure_nib_shared(h_nib & PAGE_MASK, kvm->arch.gmap)) {
+ vfio_unpin_pages(&q->matrix_mdev->vdev, nib, 1);
+ status.response_code = AP_RESPONSE_INVALID_ADDRESS;
+ return status;
+ }
+
nisc = kvm_s390_gisc_register(kvm, isc);
if (nisc < 0) {
VFIO_AP_DBF_WARN("%s: gisc registration failed: nisc=%d, isc=%d, apqn=%#04x\n",
--
2.39.3