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

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Message-Id: <20230815184333.6554-13-akrowiak@linux.ibm.com>
Date:   Tue, 15 Aug 2023 14:43:33 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     jjherne@...ux.ibm.com, freude@...ux.ibm.com,
        borntraeger@...ibm.com, cohuck@...hat.com, mjrosato@...ux.ibm.com,
        pasic@...ux.ibm.com, alex.williamson@...hat.com,
        kwankhede@...dia.com, fiuczy@...ux.ibm.com,
        Janosch Frank <frankja@...ux.ibm.com>,
        Viktor Mihajlovski <mihajlov@...ux.ibm.com>
Subject: [PATCH 12/12] s390/vfio-ap: Make sure nib is shared

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@...ux.ibm.com>
Signed-off-by: Tony Krowiak <akrowiak@...ux.ibm.com>
Acked-by: Halil Pasic <pasic@...ux.ibm.com>
Tested-by: Viktor Mihajlovski <mihajlov@...ux.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