Re: some updates of xencrash

[Dave Anderson <anderson@xxxxxxxxxx>]

Itsuro ODA wrote:
> Hi,
>
> The attached is some fixes which are necessary for xencrash to use
> for the newer version of xen (after 3.1.0, ex. 3.1.2, 3.2.0).
>
> * x86
>   - add some symbols which are used to know the boundary
>     condition at the tracing in 'bt'.
>   - fix for the symbol 'idle_pg_table_l3' going away.
>
> * x86_64
>   - fix for the virtual address area of xen code/data is added.
>   - fix for the symbol 'idle_pg_table_l4' going away.
>   - add the option '--xen_phys_start_mfn='
>     newer version of xen (ex. RHEL5.2, 3.2.0) moves the
>     physical(machine) address of xen code/data area after 
>     the system started up.
>     The relocated physical(machine) address of xen code/data
>     area is necessary to use xencrash.
>     The value can be got by 'cat /proc/iomem' under dom0.
>     -------------------------------------------------------
>     # cat /proc/iomem
>     ...
>       7e600000-7f5fffff : Hypervisor code and data  *** this line
>     ...
>     -------------------------------------------------------
>     ex. to use xencrash:
>     # crash --xen_phys_start_mfn=0x7e600 xen-syms vmcore
>   - extract 'xen_phys_start_mfn' from the XEN_ELFNOTE_CRASH_INFO
>     ElfNote.
>     This is experimental code because it is necessary to modify
>     the xen to add the xen_phys_start_mfn value in the ElfNote
>     at crash time. (the patch is also attached in this mail.)
>     A sample dump is availavle in the following URL:
>     http://people.valinux.co.jp/~oda/x86_64_dump_080417.tar.gz
>
> This patch is for crash-4.0-6.2.
>
> Thanks.
> Itsuro Oda

Hi Itsuro,

Thanks very much for the quick response.

I have one relatively minor issue.  I understand that the previously existing
"--p2m_mfn" option was expressed as an mfn, and that made sense because its value
exists in the xen hypervisor code as an mfn value (actually a xen_pfn_t).

But it seems unnecessary to bother going through the translation of the
hypservisors's "xen_phys_start" physical address into an mfn?  And then
only to have the crash utility have to turn it back into a physical address
when it uses it?  Why not just leave it as a physical address in both the
kernel patch, and when passing it to the crash utility?

From a user's standpoint, when it's necessary to pre-determine the argument from
a hypervisor/dom0 vmcore that doesn't contain it, the xen_phys_start can be determined
by either reading /proc/iomem on the live system, where as you've shown in
the example above, it's 7e600000:

>  # cat /proc/iomem
>  ...
>    7e600000-7f5fffff : Hypervisor code and data  *** this line
>  ...

Alternatively, the same dom0/HV kdump vmcore can be run in a crash session using
the dom0 vmlinux, where in this example vmcore, it's 0x3f000000:

crash> px xen_hypervisor_res
  xen_hypervisor_res = $3 = {
    start = 0x3f000000,
    end = 0x3fffffff,
    name = 0xffffffff8049ab72 "Hypervisor code and data",
    flags = 0x80000200,
    parent = 0xffff880000001180,
    sibling = 0x0,
    child = 0xffff8800000000a8
  }

For convenience sake, I'd prefer to just leave it as that, without
needlessly forcing the user to translate the above into an mfn, so
that they can simply enter: "crash --xen_phys_start=0x3f000000 ..."

The same thing applies to the kernel patch -- just leave it in its
natural state as a physical (machine) address.

Unfortunately it's already going to be an annoyance to have to pre-determine
the xen_phys_start value -- so why bother making it even more cryptic by
forcing the user to turn it into an mfn?

Another theoretical question -- since the /proc/iomem exports the
xen_phys_start variable to user space, is there any way it could
be handled entirely in user space by kexec-tools?

Dave


> === for x86 ===
> --- lkcd_x86_trace.c.org	2008-04-17 10:13:05.000000000 +0900
> +++ lkcd_x86_trace.c	2008-04-17 10:13:17.000000000 +0900
> @@ -1423,6 +1423,7 @@
>  		if (XEN_HYPER_MODE()) {
>  			func_name = kl_funcname(pc);
>  			if (STREQ(func_name, "idle_loop") || STREQ(func_name, "hypercall")
> +				|| STREQ(func_name, "tracing_off")
>  				|| STREQ(func_name, "handle_exception")) {
>  				UPDATE_FRAME(func_name, pc, 0, sp, bp, asp, 0, 0, bp - sp, 0);
>  				return(trace->nframes);
> @@ -1682,6 +1683,7 @@
>  		if (func_name && XEN_HYPER_MODE()) {
>  			if (STREQ(func_name, "continue_nmi") ||
>  			    STREQ(func_name, "vmx_asm_vmexit_handler") ||
> +			    STREQ(func_name, "handle_nmi_mce") ||
>  			    STREQ(func_name, "deferred_nmi")) {
>  				/* Interrupt frame */
>  				sp = curframe->fp + 4;
> --- x86.c.org	2008-04-17 10:29:21.000000000 +0900
> +++ x86.c	2008-04-17 10:31:51.000000000 +0900
> @@ -2846,7 +2846,10 @@
>  			*paddr = kvaddr - DIRECTMAP_VIRT_START;
>  			return TRUE;
>  		}
> -		pgd = (ulonglong *)symbol_value("idle_pg_table_l3");
> +		if (symbol_exists("idle_pg_table_l3"))
> +			pgd = (ulonglong *)symbol_value("idle_pg_table_l3");
> +		else
> +			pgd = (ulonglong *)symbol_value("idle_pg_table");
>  	} else {
>  		if (!vt->vmalloc_start) {
>  			*paddr = VTOP(kvaddr);
> @@ -4965,7 +4968,8 @@
>  		break;
>  
>  	case PRE_GDB:
> -		if (symbol_exists("idle_pg_table_l3")) {
> +		if (symbol_exists("create_pae_xen_mappings") ||
> +		    symbol_exists("idle_pg_table_l3")) {
>                  	machdep->flags |= PAE;
>  			PGDIR_SHIFT = PGDIR_SHIFT_3LEVEL;
>  			PTRS_PER_PTE = PTRS_PER_PTE_3LEVEL;
>
> === for x86_64 ===
> --- defs.h.org	2008-04-17 15:03:14.000000000 +0900
> +++ defs.h	2008-04-17 15:41:10.000000000 +0900
> @@ -2162,10 +2162,13 @@
>  
>  #define FILL_PML4_HYPER() { \
>  	if (!machdep->machspec->last_pml4_read) { \
> -		readmem(symbol_value("idle_pg_table_4"), KVADDR, \
> -			machdep->machspec->pml4, PAGESIZE(), "idle_pg_table_4", \
> +		unsigned long idle_pg_table = \
> +		    symbol_exists("idle_pg_table_4") ? symbol_value("idle_pg_table_4") : \
> +			symbol_value("idle_pg_table"); \
> +		readmem(idle_pg_table, KVADDR, \
> +			machdep->machspec->pml4, PAGESIZE(), "idle_pg_table", \
>  			FAULT_ON_ERROR); \
> -		machdep->machspec->last_pml4_read = symbol_value("idle_pg_table_4"); \
> +		machdep->machspec->last_pml4_read = idle_pg_table; \
>  	}\
>  }
>  
> @@ -4081,6 +4084,8 @@
>  void get_kdump_regs(struct bt_info *, ulong *, ulong *);
>  void xen_kdump_p2m_mfn(char *);
>  int is_sadump_xen(void);
> +void set_xen_phys_start_mfn(char *);
> +ulong xen_phys_start_mfn(void);
>  
>  /*
>   *  diskdump.c
> --- main.c.org	2008-04-17 15:26:37.000000000 +0900
> +++ main.c	2008-04-17 15:45:18.000000000 +0900
> @@ -48,6 +48,7 @@
>          {"no_ikconfig", 0, 0, 0},
>          {"hyper", 0, 0, 0},
>  	{"p2m_mfn", required_argument, 0, 0},
> +	{"xen_phys_start_mfn", required_argument, 0, 0},
>  	{"zero_excluded", 0, 0, 0},
>  	{"no_panic", 0, 0, 0},
>          {"more", 0, 0, 0},
> @@ -155,6 +156,9 @@
>  		        else if (STREQ(long_options[option_index].name, "p2m_mfn")) 
>  				xen_kdump_p2m_mfn(optarg);
>  
> +		        else if (STREQ(long_options[option_index].name, "xen_phys_start_mfn")) 
> +				set_xen_phys_start_mfn(optarg);
> +
>  		        else if (STREQ(long_options[option_index].name, "zero_excluded")) 
>  				*diskdump_flags |= ZERO_EXCLUDED;
>  
> --- netdump.c.org	2008-04-17 15:09:06.000000000 +0900
> +++ netdump.c	2008-04-17 15:48:44.000000000 +0900
> @@ -1521,6 +1521,8 @@
>  				 */
>  				if (!nd->xen_kdump_data->p2m_mfn)
>  					nd->xen_kdump_data->p2m_mfn = *(uptr+(words-1));
> +				if (words > 9 && !nd->xen_kdump_data->xen_phys_start_mfn)
> +					nd->xen_kdump_data->xen_phys_start_mfn = *(uptr+(words-2));
>  			}
>  		}
>  		break;
> @@ -1724,6 +1726,8 @@
>  				 */
>  	                        if (!nd->xen_kdump_data->p2m_mfn)
>  	                        	nd->xen_kdump_data->p2m_mfn = *(up+(words-1));
> +				if (words > 9 && !nd->xen_kdump_data->xen_phys_start_mfn)
> +					nd->xen_kdump_data->xen_phys_start_mfn = *(up+(words-2));
>  			}
>  		}
>                  break;
> @@ -2312,3 +2316,22 @@
>  
>  	return FALSE;
>  }
> +
> +void
> +set_xen_phys_start_mfn(char *arg)
> +{
> +	ulong value;
> +	int errflag = 0;
> +
> +	value = htol(arg, RETURN_ON_ERROR|QUIET, &errflag);
> +	if (!errflag)
> +		xen_kdump_data.xen_phys_start_mfn = value;
> +	else 
> +		error(WARNING, "invalid xen_phys_start_mfn argument: %s\n", arg);
> +}
> +
> +ulong
> +xen_phys_start_mfn(void)
> +{
> +	return nd->xen_kdump_data->xen_phys_start_mfn;
> +}
> --- netdump.h.org	2008-04-17 15:38:59.000000000 +0900
> +++ netdump.h	2008-04-17 15:39:38.000000000 +0900
> @@ -109,6 +109,7 @@
>  	ulong accesses;
>  	int p2m_frames;
>          ulong *p2m_mfn_frame_list;
> +	ulong xen_phys_start_mfn;
>  };
>  
>  #define KDUMP_P2M_INIT  (0x1)
> --- x86_64.c.org	2008-04-17 15:34:32.000000000 +0900
> +++ x86_64.c	2008-04-17 15:36:53.000000000 +0900
> @@ -1401,6 +1401,10 @@
>                  return FALSE;
>  
>  	if (XEN_HYPER_MODE()) {
> +		if (XENTEXT_VIRT_ADDR(kvaddr)) {
> +			*paddr = kvaddr - __XEN_VIRT_START + (xen_phys_start_mfn() << PAGESHIFT());
> +			return TRUE;
> +		}
>  		if (DIRECTMAP_VIRT_ADDR(kvaddr)) {
>  			*paddr = kvaddr - DIRECTMAP_VIRT_START;
>  			return TRUE;
> --- xen_hyper_defs.h.org	2008-04-17 15:31:23.000000000 +0900
> +++ xen_hyper_defs.h	2008-04-17 15:34:15.000000000 +0900
> @@ -64,6 +64,9 @@
>  #define DIRECTMAP_VIRT_START  (0xffff830000000000)
>  #define DIRECTMAP_VIRT_END    (0xffff840000000000)
>  #define PAGE_OFFSET_XEN_HYPER DIRECTMAP_VIRT_START
> +#define __XEN_VIRT_START        (0xFFFF828C80000000)
> +#define XENTEXT_VIRT_ADDR(vaddr) \
> +    (((vaddr) >= __XEN_VIRT_START) && ((vaddr) < DIRECTMAP_VIRT_START))
>  #endif
>  
>  #ifdef IA64
>
> === Xen (explanation purpose) ===
> --- include/xen/elfcore.h.org	2008-04-17 14:11:41.000000000 +0900
> +++ include/xen/elfcore.h	2008-04-17 14:11:57.000000000 +0900
> @@ -66,6 +66,7 @@
>      unsigned long xen_compile_time;
>      unsigned long tainted;
>  #ifdef CONFIG_X86
> +    unsigned long xen_phys_start_mfn;
>      unsigned long dom0_pfn_to_mfn_frame_list_list;
>  #endif
>  } crash_xen_info_t;
> --- arch/x86/crash.c.org	2008-04-17 14:12:51.000000000 +0900
> +++ arch/x86/crash.c	2008-04-17 14:13:13.000000000 +0900
> @@ -102,6 +102,7 @@
>      hvm_disable();
>  
>      info = kexec_crash_save_info();
> +    info->xen_phys_start_mfn = xen_phys_start >> PAGE_SHIFT;
>      info->dom0_pfn_to_mfn_frame_list_list =
>          arch_get_pfn_to_mfn_frame_list_list(dom0);
>  }

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