s390x/pci: add support for guests that request direct mapping

When receiving a guest mpcifc(4) or mpcifc(6) instruction without the T
bit set, treat this as a request to perform direct mapping instead of
address translation.  In order to facilitate this, pin the entirety of
guest memory into the host iommu.

Pinning for the direct mapping case is handled via vfio and its memory
listener.  Additionally, ram discard settings are inherited from vfio:
coordinated discards (e.g. virtio-mem) are allowed while uncoordinated
discards (e.g. virtio-balloon) are disabled.

Subsequent guest DMA operations are all expected to be of the format
guest_phys+sdma, allowing them to be used as lookup into the host
iommu table.

Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Message-ID: <20250226210013.238349-2-mjrosato@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

hw/s390x/s390-pci-bus.c

@@ -18,6 +18,8 @@
 #include "hw/s390x/s390-pci-inst.h"
 #include "hw/s390x/s390-pci-kvm.h"
 #include "hw/s390x/s390-pci-vfio.h"
+#include "hw/s390x/s390-virtio-ccw.h"
+#include "hw/boards.h"
 #include "hw/pci/pci_bus.h"
 #include "hw/qdev-properties.h"
 #include "hw/pci/pci_bridge.h"
@@ -724,12 +726,42 @@ void s390_pci_iommu_enable(S390PCIIOMMU *iommu)
     g_free(name);
 }
 
+void s390_pci_iommu_direct_map_enable(S390PCIIOMMU *iommu)
+{
+    MachineState *ms = MACHINE(qdev_get_machine());
+    S390CcwMachineState *s390ms = S390_CCW_MACHINE(ms);
+
+    /*
+     * For direct-mapping we must map the entire guest address space.  Rather
+     * than using an iommu, create a memory region alias that maps GPA X to
+     * IOVA X + SDMA.  VFIO will handle pinning via its memory listener.
+     */
+    g_autofree char *name = g_strdup_printf("iommu-dm-s390-%04x",
+                                            iommu->pbdev->uid);
+
+    iommu->dm_mr = g_malloc0(sizeof(*iommu->dm_mr));
+    memory_region_init_alias(iommu->dm_mr, OBJECT(&iommu->mr), name,
+                             get_system_memory(), 0,
+                             s390_get_memory_limit(s390ms));
+    iommu->enabled = true;
+    memory_region_add_subregion(&iommu->mr, iommu->pbdev->zpci_fn.sdma,
+                                iommu->dm_mr);
+}
+
 void s390_pci_iommu_disable(S390PCIIOMMU *iommu)
 {
     iommu->enabled = false;
     g_hash_table_remove_all(iommu->iotlb);
-    memory_region_del_subregion(&iommu->mr, MEMORY_REGION(&iommu->iommu_mr));
-    object_unparent(OBJECT(&iommu->iommu_mr));
+    if (iommu->dm_mr) {
+        memory_region_del_subregion(&iommu->mr, iommu->dm_mr);
+        object_unparent(OBJECT(iommu->dm_mr));
+        g_free(iommu->dm_mr);
+        iommu->dm_mr = NULL;
+    } else {
+        memory_region_del_subregion(&iommu->mr,
+                                    MEMORY_REGION(&iommu->iommu_mr));
+        object_unparent(OBJECT(&iommu->iommu_mr));
+    }
 }
 
 static void s390_pci_iommu_free(S390pciState *s, PCIBus *bus, int32_t devfn)
@@ -1145,6 +1177,7 @@ static void s390_pcihost_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
             /* Always intercept emulated devices */
             pbdev->interp = false;
             pbdev->forwarding_assist = false;
+            pbdev->rtr_avail = false;
         }
 
         if (s390_pci_msix_init(pbdev) && !pbdev->interp) {
@@ -1510,6 +1543,8 @@ static const Property s390_pci_device_properties[] = {
     DEFINE_PROP_BOOL("interpret", S390PCIBusDevice, interp, true),
     DEFINE_PROP_BOOL("forwarding-assist", S390PCIBusDevice, forwarding_assist,
                      true),
+    DEFINE_PROP_BOOL("relaxed-translation", S390PCIBusDevice, rtr_avail,
+                     true),
 };
 
 static const VMStateDescription s390_pci_device_vmstate = {

hw/s390x/s390-pci-inst.c

@@ -16,6 +16,7 @@
 #include "exec/memory.h"
 #include "qemu/error-report.h"
 #include "system/hw_accel.h"
+#include "hw/boards.h"
 #include "hw/pci/pci_device.h"
 #include "hw/s390x/s390-pci-inst.h"
 #include "hw/s390x/s390-pci-bus.h"
@@ -1008,17 +1009,25 @@ static int reg_ioat(CPUS390XState *env, S390PCIBusDevice *pbdev, ZpciFib fib,
     }
 
     /* currently we only support designation type 1 with translation */
-    if (!(dt == ZPCI_IOTA_RTTO && t)) {
+    if (t && dt != ZPCI_IOTA_RTTO) {
         error_report("unsupported ioat dt %d t %d", dt, t);
         s390_program_interrupt(env, PGM_OPERAND, ra);
         return -EINVAL;
+    } else if (!t && !pbdev->rtr_avail) {
+        error_report("relaxed translation not allowed");
+        s390_program_interrupt(env, PGM_OPERAND, ra);
+        return -EINVAL;
     }
 
     iommu->pba = pba;
     iommu->pal = pal;
     iommu->g_iota = g_iota;
 
-    s390_pci_iommu_enable(iommu);
+    if (t) {
+        s390_pci_iommu_enable(iommu);
+    } else {
+        s390_pci_iommu_direct_map_enable(iommu);
+    }
 
     return 0;
 }

hw/s390x/s390-pci-vfio.c

@@ -131,13 +131,28 @@ static void s390_pci_read_base(S390PCIBusDevice *pbdev,
     /* Store function type separately for type-specific behavior */
     pbdev->pft = cap->pft;
 
+    /*
+     * If the device is a passthrough ISM device, disallow relaxed
+     * translation.
+     */
+    if (pbdev->pft == ZPCI_PFT_ISM) {
+        pbdev->rtr_avail = false;
+    }
+
     /*
      * If appropriate, reduce the size of the supported DMA aperture reported
-     * to the guest based upon the vfio DMA limit.
+     * to the guest based upon the vfio DMA limit.  This is applicable for
+     * devices that are guaranteed to not use relaxed translation.  If the
+     * device is capable of relaxed translation then we must advertise the
+     * full aperture.  In this case, if translation is used then we will
+     * rely on the vfio DMA limit counting and use RPCIT CC1 / status 16
+     * to request that the guest free DMA mappings as necessary.
      */
-    vfio_size = pbdev->iommu->max_dma_limit << TARGET_PAGE_BITS;
-    if (vfio_size > 0 && vfio_size < cap->end_dma - cap->start_dma + 1) {
-        pbdev->zpci_fn.edma = cap->start_dma + vfio_size - 1;
+    if (!pbdev->rtr_avail) {
+        vfio_size = pbdev->iommu->max_dma_limit << TARGET_PAGE_BITS;
+        if (vfio_size > 0 && vfio_size < cap->end_dma - cap->start_dma + 1) {
+            pbdev->zpci_fn.edma = cap->start_dma + vfio_size - 1;
+        }
     }
 }
 

hw/s390x/s390-virtio-ccw.c

@@ -936,8 +936,13 @@ static void ccw_machine_9_2_instance_options(MachineState *machine)
 
 static void ccw_machine_9_2_class_options(MachineClass *mc)
 {
+    static GlobalProperty compat[] = {
+        { TYPE_S390_PCI_DEVICE, "relaxed-translation", "off", },
+    };
+
     ccw_machine_10_0_class_options(mc);
     compat_props_add(mc->compat_props, hw_compat_9_2, hw_compat_9_2_len);
+    compat_props_add(mc->compat_props, compat, G_N_ELEMENTS(compat));
 }
 DEFINE_CCW_MACHINE(9, 2);
 

include/hw/s390x/s390-pci-bus.h

@@ -277,6 +277,7 @@ struct S390PCIIOMMU {
     AddressSpace as;
     MemoryRegion mr;
     IOMMUMemoryRegion iommu_mr;
+    MemoryRegion *dm_mr;
     bool enabled;
     uint64_t g_iota;
     uint64_t pba;
@@ -362,6 +363,7 @@ struct S390PCIBusDevice {
     bool interp;
     bool forwarding_assist;
     bool aif;
+    bool rtr_avail;
     QTAILQ_ENTRY(S390PCIBusDevice) link;
 };
 
@@ -389,6 +391,7 @@ int pci_chsc_sei_nt2_have_event(void);
 void s390_pci_sclp_configure(SCCB *sccb);
 void s390_pci_sclp_deconfigure(SCCB *sccb);
 void s390_pci_iommu_enable(S390PCIIOMMU *iommu);
+void s390_pci_iommu_direct_map_enable(S390PCIIOMMU *iommu);
 void s390_pci_iommu_disable(S390PCIIOMMU *iommu);
 void s390_pci_generate_error_event(uint16_t pec, uint32_t fh, uint32_t fid,
                                    uint64_t faddr, uint32_t e);