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SubjectRe: [Xen-devel] [PATCH] xen pv-on-hvm: add pfn_is_ram helper for kdump
On Thu, Jul 12, 2012 at 11:00:05AM +0200, Olaf Hering wrote:
> 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.

What about the 'unregister_oldmem_pfn_is_ram' call? Should this
be implemented here as well?

Comments below.

>
> 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@aepfle.de>
> ---
> 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>

Should this also have an #idef CONFIG_PROC_VMCORE?
Or is it going to compile OK without CONFIG_PROC_VMCORE defined?

>
> #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

s/wether/whether

> + * was a ballooned page. vmcore is using this function to decide
> + * wether to access a pfn of the crashed kernel.

s/wether/wheter

> + * - the kexec kernel has to check wether a pfn was ballooned by the

Ditto.

> + * previous kernel. If the pfn is ballooned, handle it properly.

. and by handle it properly you mean return -ENXIO?

> + * 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;

Can you make this have already initialized values, like:

struct xen_hvm_get_mem_type a = {
.domid = DOMID_SELF;
.pfn = pfn
};

Also is this hypercall new? Or has it been in existence for some time?

> + 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
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel


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