[Qemu-devel] [PATCH v7 1/4] spapr_iommu: Make in-kernel TCE table optional

[Alexey Kardashevskiy]

POWER KVM supports an KVM_CAP_SPAPR_TCE capability which allows allocating
TCE tables in the host kernel memory and handle H_PUT_TCE requests
targeted to specific LIOBN (logical bus number) right in the host without
switching to QEMU. At the moment this is used for emulated devices only
and the handler only puts TCE to the table. If the in-kernel H_PUT_TCE
handler finds a LIOBN and corresponding table, it will put a TCE to
the table and complete hypercall execution. The user space will not be
notified.

Upcoming VFIO support is going to use the same sPAPRTCETable device class
so KVM_CAP_SPAPR_TCE is going to be used as well. That means that TCE
tables for VFIO are going to be allocated in the host as well.
However VFIO operates with real IOMMU tables and simple copying of
a TCE to the real hardware TCE table will not work as guest physical
to host physical address translation is requited.

So until the host kernel gets VFIO support for H_PUT_TCE, we better not
to register VFIO's TCE in the host.

This adds a bool @kvm_accel flag to the sPAPRTCETable device telling
that sPAPRTCETable should not try allocating TCE table in the host kernel.
Instead, the table will be created in QEMU.

This adds an kvm_accel parameter to spapr_tce_new_table() to let users
choose whether to use acceleration or not. At the moment it is enabled
for VIO and emulated PCI. Upcoming VFIO support will set it to false.

Signed-off-by: Alexey Kardashevskiy <address@hidden>
---

This is a workaround but it lets me have one IOMMU device for VIO, emulated
PCI and VFIO which is a good thing.

The other way around would be a new KVM_CAP_SPAPR_TCE_VFIO capability but
this needs kernel update.
---
 hw/ppc/spapr_iommu.c   | 6 ++++--
 hw/ppc/spapr_pci.c     | 2 +-
 hw/ppc/spapr_vio.c     | 2 +-
 include/hw/ppc/spapr.h | 4 +++-
 4 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/hw/ppc/spapr_iommu.c b/hw/ppc/spapr_iommu.c
index 3b6e373..bfd3701 100644
--- a/hw/ppc/spapr_iommu.c
+++ b/hw/ppc/spapr_iommu.c
@@ -115,7 +115,7 @@ static int spapr_tce_table_realize(DeviceState *dev)
 {
     sPAPRTCETable *tcet = SPAPR_TCE_TABLE(dev);
 
-    if (kvm_enabled()) {
+    if (tcet->kvm_accel && kvm_enabled()) {
         tcet->table = kvmppc_create_spapr_tce(tcet->liobn,
                                               tcet->nb_table <<
                                               tcet->page_shift,
@@ -143,7 +143,8 @@ static int spapr_tce_table_realize(DeviceState *dev)
 sPAPRTCETable *spapr_tce_new_table(DeviceState *owner, uint32_t liobn,
                                    uint64_t bus_offset,
                                    uint32_t page_shift,
-                                   uint32_t nb_table)
+                                   uint32_t nb_table,
+                                   bool kvm_accel)
 {
     sPAPRTCETable *tcet;
 
@@ -162,6 +163,7 @@ sPAPRTCETable *spapr_tce_new_table(DeviceState *owner, 
uint32_t liobn,
     tcet->bus_offset = bus_offset;
     tcet->page_shift = page_shift;
     tcet->nb_table = nb_table;
+    tcet->kvm_accel = kvm_accel;
 
     object_property_add_child(OBJECT(owner), "tce-table", OBJECT(tcet), NULL);
 
diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
index ddfd8bb..6021f35 100644
--- a/hw/ppc/spapr_pci.c
+++ b/hw/ppc/spapr_pci.c
@@ -658,7 +658,7 @@ static void spapr_phb_finish_realize(sPAPRPHBState *sphb, 
Error **errp)
     tcet = spapr_tce_new_table(DEVICE(sphb), sphb->dma_liobn,
                                0,
                                SPAPR_TCE_PAGE_SHIFT,
-                               0x40000000 >> SPAPR_TCE_PAGE_SHIFT);
+                               0x40000000 >> SPAPR_TCE_PAGE_SHIFT, true);
     if (!tcet) {
         error_setg(errp, "Unable to create TCE table for %s",
                    sphb->dtbusname);
diff --git a/hw/ppc/spapr_vio.c b/hw/ppc/spapr_vio.c
index 48b0125..16385e4 100644
--- a/hw/ppc/spapr_vio.c
+++ b/hw/ppc/spapr_vio.c
@@ -460,7 +460,7 @@ static int spapr_vio_busdev_init(DeviceState *qdev)
                                         0,
                                         SPAPR_TCE_PAGE_SHIFT,
                                         pc->rtce_window_size >>
-                                        SPAPR_TCE_PAGE_SHIFT);
+                                        SPAPR_TCE_PAGE_SHIFT, true);
         address_space_init(&dev->as, spapr_tce_get_iommu(dev->tcet), qdev->id);
     }
 
diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
index 4ffb903..7db34ff 100644
--- a/include/hw/ppc/spapr.h
+++ b/include/hw/ppc/spapr.h
@@ -402,6 +402,7 @@ struct sPAPRTCETable {
     uint32_t page_shift;
     uint64_t *table;
     bool bypass;
+    bool kvm_accel;
     int fd;
     MemoryRegion iommu;
     QLIST_ENTRY(sPAPRTCETable) list;
@@ -413,7 +414,8 @@ int spapr_h_cas_compose_response(target_ulong addr, 
target_ulong size);
 sPAPRTCETable *spapr_tce_new_table(DeviceState *owner, uint32_t liobn,
                                    uint64_t bus_offset,
                                    uint32_t page_shift,
-                                   uint32_t nb_table);
+                                   uint32_t nb_table,
+                                   bool kvm_accel);
 MemoryRegion *spapr_tce_get_iommu(sPAPRTCETable *tcet);
 void spapr_tce_set_bypass(sPAPRTCETable *tcet, bool bypass);
 int spapr_dma_dt(void *fdt, int node_off, const char *propname,
-- 
2.0.0