How can show_page_walk() be called before paging_init() sets up the M2P
table? It is invoked only from exception and interrupt handlers, which are
not installed until trap_init() has run. And trap_init() is invoked later
than paging_init() during boot.
-- Keir
On 24/1/08 15:03, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:
> While adding 1Gb page support for the 1:1 mapping I noticed that
> show_page_walk() crashes when used before the M2P table gets created,
> and from looking at the code I realized that it would also crash if a
> corrupt page table with an out of range MFN would be encountered.
> While it would have been possible to make get_gpfn_from_mfn() more
> robust, it seemed like keeping the overhead there low (as in the
> general case proper values can be expected and would likely have been
> checked for already), and hence I made the checks privates to
> show_page_walk().
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
>
> Index: 2008-01-18/xen/arch/x86/x86_32/mm.c
> ===================================================================
> --- 2008-01-18.orig/xen/arch/x86/x86_32/mm.c 2008-01-23 11:54:09.000000000
> +0100
> +++ 2008-01-18/xen/arch/x86/x86_32/mm.c 2008-01-23 11:48:16.000000000 +0100
> @@ -41,6 +41,7 @@ l2_pgentry_t __attribute__ ((__section__
> unsigned int PAGE_HYPERVISOR = __PAGE_HYPERVISOR;
> unsigned int PAGE_HYPERVISOR_NOCACHE = __PAGE_HYPERVISOR_NOCACHE;
>
> +int mpt_valid;
> static unsigned long mpt_size;
>
> void *alloc_xen_pagetable(void)
> @@ -110,6 +111,8 @@ void __init paging_init(void)
> pg, (__PAGE_HYPERVISOR | _PAGE_PSE) & ~_PAGE_RW));
> }
>
> + mpt_valid = 1;
> +
> /* Fill with an obvious debug pattern. */
> for ( i = 0; i < (mpt_size / BYTES_PER_LONG); i++)
> set_gpfn_from_mfn(i, 0x55555555);
> Index: 2008-01-18/xen/arch/x86/x86_32/traps.c
> ===================================================================
> --- 2008-01-18.orig/xen/arch/x86/x86_32/traps.c 2008-01-23 11:54:09.000000000
> +0100
> +++ 2008-01-18/xen/arch/x86/x86_32/traps.c 2008-01-23 11:53:58.000000000 +0100
> @@ -132,7 +132,8 @@ void show_page_walk(unsigned long addr)
> l3t += (cr3 & 0xFE0UL) >> 3;
> l3e = l3t[l3_table_offset(addr)];
> mfn = l3e_get_pfn(l3e);
> - pfn = get_gpfn_from_mfn(mfn);
> + pfn = mfn_valid(mfn) && mpt_valid ?
> + get_gpfn_from_mfn(mfn) : INVALID_M2P_ENTRY;
> printk(" L3[0x%03lx] = %"PRIpte" %08lx\n",
> l3_table_offset(addr), l3e_get_intpte(l3e), pfn);
> unmap_domain_page(l3t);
> @@ -143,7 +144,8 @@ void show_page_walk(unsigned long addr)
> l2t = map_domain_page(mfn);
> l2e = l2t[l2_table_offset(addr)];
> mfn = l2e_get_pfn(l2e);
> - pfn = get_gpfn_from_mfn(mfn);
> + pfn = mfn_valid(mfn) && mpt_valid ?
> + get_gpfn_from_mfn(mfn) : INVALID_M2P_ENTRY;
> printk(" L2[0x%03lx] = %"PRIpte" %08lx %s\n",
> l2_table_offset(addr), l2e_get_intpte(l2e), pfn,
> (l2e_get_flags(l2e) & _PAGE_PSE) ? "(PSE)" : "");
> @@ -155,7 +157,8 @@ void show_page_walk(unsigned long addr)
> l1t = map_domain_page(mfn);
> l1e = l1t[l1_table_offset(addr)];
> mfn = l1e_get_pfn(l1e);
> - pfn = get_gpfn_from_mfn(mfn);
> + pfn = mfn_valid(mfn) && mpt_valid ?
> + get_gpfn_from_mfn(mfn) : INVALID_M2P_ENTRY;
> printk(" L1[0x%03lx] = %"PRIpte" %08lx\n",
> l1_table_offset(addr), l1e_get_intpte(l1e), pfn);
> unmap_domain_page(l1t);
> Index: 2008-01-18/xen/arch/x86/x86_64/mm.c
> ===================================================================
> --- 2008-01-18.orig/xen/arch/x86/x86_64/mm.c 2008-01-23 11:54:09.000000000
> +0100
> +++ 2008-01-18/xen/arch/x86/x86_64/mm.c 2008-01-23 11:50:56.000000000 +0100
> @@ -32,6 +32,7 @@
> #include <asm/msr.h>
> #include <public/memory.h>
>
> +int mpt_valid;
> #ifdef CONFIG_COMPAT
> unsigned int m2p_compat_vstart = __HYPERVISOR_COMPAT_VIRT_START;
> #endif
> @@ -144,6 +145,8 @@ void __init paging_init(void)
> l2_ro_mpt++;
> }
>
> + mpt_valid = 1;
> +
> /* Create user-accessible L2 directory to map the MPT for compat guests.
> */
> BUILD_BUG_ON(l4_table_offset(RDWR_MPT_VIRT_START) !=
> l4_table_offset(HIRO_COMPAT_MPT_VIRT_START));
> Index: 2008-01-18/xen/arch/x86/x86_64/traps.c
> ===================================================================
> --- 2008-01-18.orig/xen/arch/x86/x86_64/traps.c 2008-01-23 11:54:09.000000000
> +0100
> +++ 2008-01-18/xen/arch/x86/x86_64/traps.c 2008-01-23 11:53:27.000000000 +0100
> @@ -136,7 +136,8 @@ void show_page_walk(unsigned long addr)
> l4t = mfn_to_virt(mfn);
> l4e = l4t[l4_table_offset(addr)];
> mfn = l4e_get_pfn(l4e);
> - pfn = get_gpfn_from_mfn(mfn);
> + pfn = mfn_valid(mfn) && mpt_valid ?
> + get_gpfn_from_mfn(mfn) : INVALID_M2P_ENTRY;
> printk(" L4[0x%03lx] = %"PRIpte" %016lx\n",
> l4_table_offset(addr), l4e_get_intpte(l4e), pfn);
> if ( !(l4e_get_flags(l4e) & _PAGE_PRESENT) )
> @@ -145,7 +146,8 @@ void show_page_walk(unsigned long addr)
> l3t = mfn_to_virt(mfn);
> l3e = l3t[l3_table_offset(addr)];
> mfn = l3e_get_pfn(l3e);
> - pfn = get_gpfn_from_mfn(mfn);
> + pfn = mfn_valid(mfn) && mpt_valid ?
> + get_gpfn_from_mfn(mfn) : INVALID_M2P_ENTRY;
> printk(" L3[0x%03lx] = %"PRIpte" %016lx\n",
> l3_table_offset(addr), l3e_get_intpte(l3e), pfn);
> if ( !(l3e_get_flags(l3e) & _PAGE_PRESENT) )
> @@ -154,7 +156,8 @@ void show_page_walk(unsigned long addr)
> l2t = mfn_to_virt(mfn);
> l2e = l2t[l2_table_offset(addr)];
> mfn = l2e_get_pfn(l2e);
> - pfn = get_gpfn_from_mfn(mfn);
> + pfn = mfn_valid(mfn) && mpt_valid ?
> + get_gpfn_from_mfn(mfn) : INVALID_M2P_ENTRY;
> printk(" L2[0x%03lx] = %"PRIpte" %016lx %s\n",
> l2_table_offset(addr), l2e_get_intpte(l2e), pfn,
> (l2e_get_flags(l2e) & _PAGE_PSE) ? "(PSE)" : "");
> @@ -165,7 +168,8 @@ void show_page_walk(unsigned long addr)
> l1t = mfn_to_virt(mfn);
> l1e = l1t[l1_table_offset(addr)];
> mfn = l1e_get_pfn(l1e);
> - pfn = get_gpfn_from_mfn(mfn);
> + pfn = mfn_valid(mfn) && mpt_valid ?
> + get_gpfn_from_mfn(mfn) : INVALID_M2P_ENTRY;
> printk(" L1[0x%03lx] = %"PRIpte" %016lx\n",
> l1_table_offset(addr), l1e_get_intpte(l1e), pfn);
> }
> Index: 2008-01-18/xen/include/asm-x86/mm.h
> ===================================================================
> --- 2008-01-18.orig/xen/include/asm-x86/mm.h 2008-01-23 11:54:09.000000000
> +0100
> +++ 2008-01-18/xen/include/asm-x86/mm.h 2008-01-23 11:55:37.000000000 +0100
> @@ -267,6 +267,7 @@ TYPE_SAFE(unsigned long,mfn);
> #define machine_to_phys_mapping ((unsigned long *)RDWR_MPT_VIRT_START)
> #define INVALID_M2P_ENTRY (~0UL)
> #define VALID_M2P(_e) (!((_e) & (1UL<<(BITS_PER_LONG-1))))
> +extern int mpt_valid;
>
> #ifdef CONFIG_COMPAT
> #define compat_machine_to_phys_mapping ((unsigned int
> *)RDWR_COMPAT_MPT_VIRT_START)
>
>
>
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> http://lists.xensource.com/xen-devel
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