[Qemu-devel] [PATCH] target-ppc: explicitly save page table headers in big endian

[Qemu-devel] [PATCH] target-ppc: explicitly save page table headers in big endian

[Cédric Le Goater]

Currently, when the page tables are saved, the kvm_get_htab_header structs 
and the ptes are assumed being big endian and dumped as a indistinct blob 
in the statefile. This is no longer true when the host is little endian 
and this breaks restoration.

This patch unfolds the kvmppc_save_htab routine to write explicitly the 
kvm_get_htab_header structs in big endian. The ptes are left untouched.

Signed-off-by: Cédric Le Goater <clg@fr.ibm.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: Gregory Kurz <gkurz@linux.vnet.ibm.com>

---

 This patch needs to be completed by a relatively simple modification of
 kvm_htab_write() in the kvm_hv kernel mmodule. 

 Tested on 3.17-rc7 with LE and BE host, and with a cross endian gdb.

 target-ppc/kvm.c |   20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

Index: qemu.git/target-ppc/kvm.c
===================================================================
--- qemu.git.orig/target-ppc/kvm.c
+++ qemu.git/target-ppc/kvm.c
@@ -2246,8 +2246,23 @@ int kvmppc_save_htab(QEMUFile *f, int fd
                     strerror(errno));
             return rc;
         } else if (rc) {
-            /* Kernel already retuns data in BE format for the file */
-            qemu_put_buffer(f, buf, rc);
+            uint8_t *buffer = buf;
+            ssize_t n = rc;
+            while (n) {
+                struct kvm_get_htab_header *head =
+                    (struct kvm_get_htab_header *) buffer;
+                size_t chunksize = sizeof(*head) +
+                     HASH_PTE_SIZE_64 * head->n_valid;
+
+                qemu_put_be32(f, head->index);
+                qemu_put_be16(f, head->n_valid);
+                qemu_put_be16(f, head->n_invalid);
+                qemu_put_buffer(f, (void *)(head + 1),
+                                HASH_PTE_SIZE_64 * head->n_valid);
+
+                buffer += chunksize;
+                n -= chunksize;
+            }
         }
     } while ((rc != 0)
              && ((max_ns < 0)
@@ -2264,7 +2279,6 @@ int kvmppc_load_htab_chunk(QEMUFile *f,
     ssize_t rc;
 
     buf = alloca(chunksize);
-    /* This is KVM on ppc, so this is all big-endian */
     buf->index = index;
     buf->n_valid = n_valid;
     buf->n_invalid = n_invalid;

Re: [Qemu-devel] [PATCH] target-ppc: explicitly save page table headers in big endian

[Alexander Graf]

On 03.11.14 16:14, Cédric Le Goater wrote:
> Currently, when the page tables are saved, the kvm_get_htab_header structs 
> and the ptes are assumed being big endian and dumped as a indistinct blob 
> in the statefile. This is no longer true when the host is little endian 
> and this breaks restoration.
> 
> This patch unfolds the kvmppc_save_htab routine to write explicitly the 
> kvm_get_htab_header structs in big endian. The ptes are left untouched.
> 
> Signed-off-by: Cédric Le Goater <clg@fr.ibm.com>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Alexey Kardashevskiy <aik@ozlabs.ru>
> Cc: Gregory Kurz <gkurz@linux.vnet.ibm.com>

Thanks, applied to ppc-next-2.3.


Alex