[Xen-devel] [PATCH] xen pv-on-hvm: add pfn_is_ram helper for kdump

[Olaf Hering <olaf@xxxxxxxxx>]

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.

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.

Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
---
 arch/x86/xen/mmu.c |   39 +++++++++++++++++++++++++++++++++++++++
 1 files changed, 39 insertions(+), 0 deletions(-)

diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 3a73785..ac876c2 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>
 
@@ -2245,6 +2246,41 @@ 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 wether a pfn of the crashed kernel
+ *   was a ballooned page. vmcore is using this function to decide
+ *   wether to access a pfn of the crashed kernel.
+ * - the kexec kernel has to check wether 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.
+ */
+static int xen_oldmem_pfn_is_ram(unsigned long pfn)
+{
+       struct xen_hvm_get_mem_type a;
+       int ram;
+
+       a.domid = DOMID_SELF;
+       a.pfn = pfn;
+       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;
@@ -2275,6 +2311,9 @@ 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
 
-- 
1.7.3.4


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