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

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Thu, Jul 12, 2012 at 07:20:39PM +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.
> 
> 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>
> ---
>  arch/x86/xen/mmu.c                 |   41 ++++++++++++++++++++++++++++++++++++
>  include/xen/interface/hvm/hvm_op.h |   20 ++++++++++++++++++
>  2 Dateien geändert, 61 Zeilen hinzugefügt(+)
> 
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index 3a73785..54de84d 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 +2246,43 @@ 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;
> @@ -2275,6 +2313,9 @@ 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..0816ae4 100644
> --- a/include/xen/interface/hvm/hvm_op.h
> +++ b/include/xen/interface/hvm/hvm_op.h
> @@ -43,4 +43,24 @@ 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);
>   
> +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;

Does this have to be a typdef?

> +
> +#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;

Please no typdefs. I can fix this up, but in the future pls don't add
more of them.


> +DEFINE_GUEST_HANDLE_STRUCT(xen_hvm_get_mem_type_t);
> +
>  #endif /* __XEN_PUBLIC_HVM_HVM_OP_H__ */
> -- 
> 1.7.10.4
> 
> 
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