[PATCH 3/5] s390x/pci: Shrink RPCIT ranges to registered window

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

From: Matthew Rosato <mjrosato@linux.ibm.com>

Today, if a RPCIT instruction is presented from the guest whose range
exceeds the previously-registered IOAT, QEMU will process the range
so long as 1) the specified range at least partially overlaps with
what was previously registered and 2) the guest has valid IOAT entries
in its table.  If the entries are not present (invalid), then the
RPCIT will unnecessarily spend time reporting the invalid
region/segment entries.

Optimize this path by exiting immediately if the requested range falls
completely outside of the previously-registered range or if the
requested range ends before it starts (which would only occur if the
guest-specified address + length would overflow a u64).  Otherwise,
clamp the request to only the portion of the range that overlaps with
what was previously registered, effectively ignoring the portion
outside of the registered range.

Cc: qemu-stable@nongnu.org
Fixes: 5d1abf2344 ("s390x/pci: enforce zPCI state checking")
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
---
 hw/s390x/s390-pci-inst.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/hw/s390x/s390-pci-inst.c b/hw/s390x/s390-pci-inst.c
index ef20f7645e..b7de23c7d2 100644
--- a/hw/s390x/s390-pci-inst.c
+++ b/hw/s390x/s390-pci-inst.c
@@ -770,10 +770,16 @@ int rpcit_service_call(S390CPU *cpu, uint8_t r1, uint8_t r2, uintptr_t ra)
         goto err;
     }
 
-    if (end < iommu->pba || start > iommu->pal) {
+    if (end < start || end < iommu->pba || start > iommu->pal) {
         error = ERR_EVENT_OORANGE;
         goto err;
     }
+    /*
+     * If the specified range at least partially overlaps the registered
+     * aperture, clamp the request to the aperture and ignore the rest.
+     */
+    sstart = MAX(start, iommu->pba);
+    end = MIN(end, iommu->pal + 1);
 
  retry:
     start = sstart;
-- 
2.53.0