Register pfn_is_ram helper speed up reading /proc/vmcore in the kdump
kernel. See commit message of 997c136f518c ("fs/proc/vmcore.c: add hook
to read_from_oldmem() to check for non-ram pages") for details.
It makes use of a new hvmop HVMOP_get_mem_type which was introduced in
xen 4.2 (23298:26413986e6e0) and backported to 4.1.1.
The new function is currently only enabled for reading /proc/vmcore.
Later it will be used also for the kexec kernel. Since that requires
more changes in the generic kernel make it static for the time being.
Signed-off-by: Olaf Hering <olaf@aepfle.de>
---
v2:
- remove typedefs
arch/x86/xen/mmu.c | 41 ++++++++++++++++++++++++++++++++++++++
include/xen/interface/hvm/hvm_op.h | 19 ++++++++++++++++++
2 files changed, 60 insertions(+)
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 5141d80..973962a 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -47,6 +47,7 @@
#include <linux/gfp.h>
#include <linux/memblock.h>
#include <linux/seq_file.h>
+#include <linux/crash_dump.h>
#include <trace/events/xen.h>
@@ -2272,6 +2273,43 @@ void xen_destroy_contiguous_region(unsigned long vstart,
unsigned int order)
EXPORT_SYMBOL_GPL(xen_destroy_contiguous_region);
#ifdef CONFIG_XEN_PVHVM
+#ifdef CONFIG_PROC_VMCORE
+/*
+ * This function is used in two contexts:
+ * - the kdump kernel has to check whether a pfn of the crashed kernel
+ * was a ballooned page. vmcore is using this function to decide
+ * whether to access a pfn of the crashed kernel.
+ * - the kexec kernel has to check whether a pfn was ballooned by the
+ * previous kernel. If the pfn is ballooned, handle it properly.
+ * Returns 0 if the pfn is not backed by a RAM page, the caller may
+ * handle the pfn special in this case.
+ */
+static int xen_oldmem_pfn_is_ram(unsigned long pfn)
+{
+ struct xen_hvm_get_mem_type a = {
+ .domid = DOMID_SELF,
+ .pfn = pfn,
+ };
+ int ram;
+
+ if (HYPERVISOR_hvm_op(HVMOP_get_mem_type, &a))
+ return -ENXIO;
+
+ switch (a.mem_type) {
+ case HVMMEM_mmio_dm:
+ ram = 0;
+ break;
+ case HVMMEM_ram_rw:
+ case HVMMEM_ram_ro:
+ default:
+ ram = 1;
+ break;
+ }
+
+ return ram;
+}
+#endif
+
static void xen_hvm_exit_mmap(struct mm_struct *mm)
{
struct xen_hvm_pagetable_dying a;
@@ -2302,6 +2340,9 @@ void __init xen_hvm_init_mmu_ops(void)
{
if (is_pagetable_dying_supported())
pv_mmu_ops.exit_mmap = xen_hvm_exit_mmap;
+#ifdef CONFIG_PROC_VMCORE
+ register_oldmem_pfn_is_ram(&xen_oldmem_pfn_is_ram);
+#endif
}
#endif
diff --git a/include/xen/interface/hvm/hvm_op.h
b/include/xen/interface/hvm/hvm_op.h
index a4827f4..956a046 100644
--- a/include/xen/interface/hvm/hvm_op.h
+++ b/include/xen/interface/hvm/hvm_op.h
@@ -43,4 +43,23 @@ struct xen_hvm_pagetable_dying {
typedef struct xen_hvm_pagetable_dying xen_hvm_pagetable_dying_t;
DEFINE_GUEST_HANDLE_STRUCT(xen_hvm_pagetable_dying_t);
+enum hvmmem_type_t {
+ 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 */
+};
+
+#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;
+};
+DEFINE_GUEST_HANDLE_STRUCT(xen_hvm_get_mem_type);
+
#endif /* __XEN_PUBLIC_HVM_HVM_OP_H__ */
--
1.7.12