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[Qemu-devel] [PULL 22/25] spapr: Limit available pagesizes to provide a


From: David Gibson
Subject: [Qemu-devel] [PULL 22/25] spapr: Limit available pagesizes to provide a consistent guest environment
Date: Fri, 22 Jun 2018 20:35:25 +1000

KVM HV has some limitations (deriving from the hardware) that mean not all
host-cpu supported pagesizes may be usable in the guest.  At present this
means that KVM guests and TCG guests may see different available page sizes
even if they notionally have the same vcpu model.  This is confusing and
also prevents migration between TCG and KVM.

This patch makes the environment consistent by always allowing the same set
of pagesizes.  Since we can't remove the KVM limitations, we do this by
always applying the same limitations it has, even to TCG guests.

Signed-off-by: David Gibson <address@hidden>
Reviewed-by: C├ędric Le Goater <address@hidden>
Reviewed-by: Greg Kurz <address@hidden>
---
 hw/ppc/spapr_caps.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
index 722b213d9a..62663ebdf5 100644
--- a/hw/ppc/spapr_caps.c
+++ b/hw/ppc/spapr_caps.c
@@ -335,6 +335,39 @@ static void cap_hpt_maxpagesize_apply(sPAPRMachineState 
*spapr,
     spapr_check_pagesize(spapr, qemu_getrampagesize(), errp);
 }
 
+static bool spapr_pagesize_cb(void *opaque, uint32_t seg_pshift,
+                              uint32_t pshift)
+{
+    unsigned maxshift = *((unsigned *)opaque);
+
+    assert(pshift >= seg_pshift);
+
+    /* Don't allow the guest to use pages bigger than the configured
+     * maximum size */
+    if (pshift > maxshift) {
+        return false;
+    }
+
+    /* For whatever reason, KVM doesn't allow multiple pagesizes
+     * within a segment, *except* for the case of 16M pages in a 4k or
+     * 64k segment.  Always exclude other cases, so that TCG and KVM
+     * guests see a consistent environment */
+    if ((pshift != seg_pshift) && (pshift != 24)) {
+        return false;
+    }
+
+    return true;
+}
+
+static void cap_hpt_maxpagesize_cpu_apply(sPAPRMachineState *spapr,
+                                          PowerPCCPU *cpu,
+                                          uint8_t val, Error **errp)
+{
+    unsigned maxshift = val;
+
+    ppc_hash64_filter_pagesizes(cpu, spapr_pagesize_cb, &maxshift);
+}
+
 sPAPRCapabilityInfo capability_table[SPAPR_CAP_NUM] = {
     [SPAPR_CAP_HTM] = {
         .name = "htm",
@@ -402,6 +435,7 @@ sPAPRCapabilityInfo capability_table[SPAPR_CAP_NUM] = {
         .set = spapr_cap_set_pagesize,
         .type = "int",
         .apply = cap_hpt_maxpagesize_apply,
+        .cpu_apply = cap_hpt_maxpagesize_cpu_apply,
     },
 };
 
-- 
2.17.1




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