[Qemu-devel] [RFC for-2.13 1/7] spapr: Maximum (HPT) pagesize property

[David Gibson <david@gibson.dropbear.id.au>]

The way the POWER Hash Page Table (HPT) MMU is virtualized by KVM HV means
that every page that the guest puts in the pagetables must be truly
physically contiguous, not just GPA-contiguous.  In effect this means that
an HPT guest can't use any pagesizes greater than the host page size used
to back its memory.

At present we handle this by changing what we advertise to the guest based
on the backing pagesizes.  This is pretty bad, because it means the guest
sees a different environment depending on what should be host configuration
details.

As a start on fixing this, we add a new capability parameter to the pseries
machine type which gives the maximum allowed pagesizes for an HPT guest (as
a shift).  For now we just create and validate the parameter without making
it do anything.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 hw/ppc/spapr.c         |  1 +
 hw/ppc/spapr_caps.c    | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++
 include/hw/ppc/spapr.h |  4 +++-
 3 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index bdf72e1e89..36e41aff71 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -3876,6 +3876,7 @@ static void spapr_machine_class_init(ObjectClass *oc, void *data)
     smc->default_caps.caps[SPAPR_CAP_CFPC] = SPAPR_CAP_BROKEN;
     smc->default_caps.caps[SPAPR_CAP_SBBC] = SPAPR_CAP_BROKEN;
     smc->default_caps.caps[SPAPR_CAP_IBS] = SPAPR_CAP_BROKEN;
+    smc->default_caps.caps[SPAPR_CAP_HPT_MPS] = 16; /* Allow 64kiB pages */
     spapr_caps_add_properties(smc, &error_abort);
 }
 
diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
index 531e145114..cbc41f5b20 100644
--- a/hw/ppc/spapr_caps.c
+++ b/hw/ppc/spapr_caps.c
@@ -27,6 +27,7 @@
 #include "qapi/visitor.h"
 #include "sysemu/hw_accel.h"
 #include "target/ppc/cpu.h"
+#include "target/ppc/mmu-hash64.h"
 #include "cpu-models.h"
 #include "kvm_ppc.h"
 
@@ -142,6 +143,39 @@ out:
     g_free(val);
 }
 
+static void spapr_cap_get_int(Object *obj, Visitor *v, const char *name,
+                               void *opaque, Error **errp)
+{
+    sPAPRCapabilityInfo *cap = opaque;
+    sPAPRMachineState *spapr = SPAPR_MACHINE(obj);
+    int64_t value = spapr_get_cap(spapr, cap->index);
+
+    visit_type_int(v, name, &value, errp);
+}
+
+static void spapr_cap_set_int(Object *obj, Visitor *v, const char *name,
+                               void *opaque, Error **errp)
+{
+    sPAPRCapabilityInfo *cap = opaque;
+    sPAPRMachineState *spapr = SPAPR_MACHINE(obj);
+    int64_t value;
+    Error *local_err = NULL;
+
+    visit_type_int(v, name, &value, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        return;
+    }
+
+    if ((value < 0) || (value > 255)) {
+        error_setg(errp, "Value for %s out of range (0..255)", name);
+        return;
+    }
+
+    spapr->cmd_line_caps[cap->index] = true;
+    spapr->eff.caps[cap->index] = value;
+}
+
 static void cap_htm_apply(sPAPRMachineState *spapr, uint8_t val, Error **errp)
 {
     if (!val) {
@@ -265,6 +299,16 @@ static void cap_safe_indirect_branch_apply(sPAPRMachineState *spapr,
 
 #define VALUE_DESC_TRISTATE     " (broken, workaround, fixed)"
 
+static void cap_hpt_mps_apply(sPAPRMachineState *spapr,
+                              uint8_t val, Error **errp)
+{
+    if (val < 12) {
+        error_setg(errp, "Require at least 4kiB pages (cap-hpt-mps >= 12)");
+    } else if (val < 16) {
+        warn_report("Many PAPR guests require 64kiB pages (cap-hpt-mps >= 16)");
+    }
+}
+
 sPAPRCapabilityInfo capability_table[SPAPR_CAP_NUM] = {
     [SPAPR_CAP_HTM] = {
         .name = "htm",
@@ -324,6 +368,15 @@ sPAPRCapabilityInfo capability_table[SPAPR_CAP_NUM] = {
         .possible = &cap_ibs_possible,
         .apply = cap_safe_indirect_branch_apply,
     },
+    [SPAPR_CAP_HPT_MPS] = {
+        .name = "hpt-mps",
+        .description = "Maximum page shift for Hash Page Table guests (12, 16, 24, 34)",
+        .index = SPAPR_CAP_HPT_MPS,
+        .get = spapr_cap_get_int,
+        .set = spapr_cap_set_int,
+        .type = "int",
+        .apply = cap_hpt_mps_apply,
+    },
 };
 
 static sPAPRCapabilities default_caps_with_cpu(sPAPRMachineState *spapr,
diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
index d60b7c6d7a..60ed3a5657 100644
--- a/include/hw/ppc/spapr.h
+++ b/include/hw/ppc/spapr.h
@@ -66,8 +66,10 @@ typedef enum {
 #define SPAPR_CAP_SBBC                  0x04
 /* Indirect Branch Serialisation */
 #define SPAPR_CAP_IBS                   0x05
+/* HPT Maximum Page Shift */
+#define SPAPR_CAP_HPT_MPS               0x06
 /* Num Caps */
-#define SPAPR_CAP_NUM                   (SPAPR_CAP_IBS + 1)
+#define SPAPR_CAP_NUM                   (SPAPR_CAP_HPT_MPS + 1)
 
 /*
  * Capability Values
-- 
2.14.3