[Xen-devel] [PATCH v2] add HVMOP_get_mem_type hvmop

[Olaf Hering <olaf@xxxxxxxxx>]

The balloon driver in the guest frees guest pages and marks them as
mmio. When the kernel crashes and the crash kernel attempts to read the
oldmem via /proc/vmcore a read from ballooned pages will generate 100%
load in dom0 because Xen asks qemu-dm for the page content. Since the
reads come in as 8byte requests each ballooned page is tried 512 times.

Add a new hvmop HVMOP_get_mem_type to return the hvmmem_type_t for the
given pfn. Pages which are neither ram or mmio will be HVMMEM_mmio_dm.
This interface enables the crash kernel to skip ballooned pages.

Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>

diff -r 10f27b8b3d63 xen/arch/ia64/vmx/vmx_hypercall.c
--- a/xen/arch/ia64/vmx/vmx_hypercall.c Mon May 02 12:00:40 2011 +0100
+++ b/xen/arch/ia64/vmx/vmx_hypercall.c Tue May 03 21:12:22 2011 +0200
@@ -217,6 +217,7 @@ do_hvm_op(unsigned long op, XEN_GUEST_HA
         break;
     }
 
+    case HVMOP_get_mem_type:
     case HVMOP_set_mem_type:
     case HVMOP_set_mem_access:
     case HVMOP_get_mem_access:
diff -r 10f27b8b3d63 xen/arch/x86/hvm/hvm.c
--- a/xen/arch/x86/hvm/hvm.c    Mon May 02 12:00:40 2011 +0100
+++ b/xen/arch/x86/hvm/hvm.c    Tue May 03 21:12:22 2011 +0200
@@ -3676,6 +3676,37 @@ long do_hvm_op(unsigned long op, XEN_GUE
         break;
     }
 
+    case HVMOP_get_mem_type:
+    {
+        struct xen_hvm_get_mem_type a;
+        struct domain *d;
+        p2m_type_t t;
+
+        if ( copy_from_guest(&a, arg, 1) )
+            return -EFAULT;
+
+        rc = rcu_lock_target_domain_by_id(a.domid, &d);
+        if ( rc != 0 )
+            return rc;
+
+        rc = -EINVAL;
+        if ( is_hvm_domain(d) )
+        {
+            gfn_to_mfn_unshare(p2m_get_hostp2m(d), a.pfn, &t, 0);
+            if ( p2m_is_mmio(t) )
+                a.mem_type =  HVMMEM_mmio_dm;
+            else if ( p2m_is_readonly(t) )
+                a.mem_type =  HVMMEM_ram_ro;
+            else if ( p2m_is_ram(t) )
+                a.mem_type =  HVMMEM_ram_rw;
+            else
+                a.mem_type =  HVMMEM_mmio_dm;
+            rc = copy_to_guest(arg, &a, 1) ? -EFAULT : 0;
+        }
+        rcu_unlock_domain(d);
+        break;
+    }
+
     case HVMOP_set_mem_type:
     {
         struct xen_hvm_set_mem_type a;
diff -r 10f27b8b3d63 xen/include/public/hvm/hvm_op.h
--- a/xen/include/public/hvm/hvm_op.h   Mon May 02 12:00:40 2011 +0100
+++ b/xen/include/public/hvm/hvm_op.h   Tue May 03 21:12:22 2011 +0200
@@ -76,6 +76,12 @@ DEFINE_XEN_GUEST_HANDLE(xen_hvm_set_pci_
 /* Flushes all VCPU TLBs: @arg must be NULL. */
 #define HVMOP_flush_tlbs          5
 
+typedef enum {
+    HVMMEM_ram_rw,             /* Normal read/write guest RAM */
+    HVMMEM_ram_ro,             /* Read-only; writes are discarded */
+    HVMMEM_mmio_dm,            /* Reads and write go to the device model */
+} hvmmem_type_t;
+
 /* Following tools-only interfaces may change in future. */
 #if defined(__XEN__) || defined(__XEN_TOOLS__)
 
@@ -109,11 +115,6 @@ typedef struct xen_hvm_modified_memory x
 DEFINE_XEN_GUEST_HANDLE(xen_hvm_modified_memory_t);
 
 #define HVMOP_set_mem_type    8
-typedef enum {
-    HVMMEM_ram_rw,             /* Normal read/write guest RAM */
-    HVMMEM_ram_ro,             /* Read-only; writes are discarded */
-    HVMMEM_mmio_dm,            /* Reads and write go to the device model */
-} hvmmem_type_t;
 /* Notify that a region of memory is to be treated in a specific way. */
 struct xen_hvm_set_mem_type {
     /* Domain to be updated. */
@@ -225,4 +226,18 @@ DEFINE_XEN_GUEST_HANDLE(xen_hvm_inject_t
 
 #endif /* defined(__XEN__) || defined(__XEN_TOOLS__) */
 
+#define HVMOP_get_mem_type    15
+/* Return hvmmem_type_t for the specified pfn. */
+struct xen_hvm_get_mem_type {
+    /* Domain to be queried. */
+    domid_t domid;
+    /* OUT variable. */
+    uint16_t mem_type;
+    uint16_t pad[2]; /* align next field on 8-byte boundary */
+    /* IN variable. */
+    uint64_t pfn;
+};
+typedef struct xen_hvm_get_mem_type xen_hvm_get_mem_type_t;
+DEFINE_XEN_GUEST_HANDLE(xen_hvm_get_mem_type_t);
+
 #endif /* __XEN_PUBLIC_HVM_HVM_OP_H__ */

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