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xen: efficiently support a holey p2m table

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When using sparsemem and memory hotplug, the kernel's pseudo-physical
address space can be discontigious.  Previously this was dealt with by
having the upper parts of the radix tree stubbed off.  Unfortunately,
this is incompatible with save/restore, which requires a complete p2m
table.

The solution is to have a special distinguished all-invalid p2m leaf
page, which we can point all the hole areas at.  This allows the tools
to see a complete p2m table, but it only costs a page for all memory
holes.

It also simplifies the code since it removes a few special cases.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Jeremy Fitzhardinge 2008-05-26 23:31:20 +01:00 committed by Thomas Gleixner
parent 8006ec3e91
commit cf0923ea29
1 changed files with 12 additions and 6 deletions
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18
arch/x86/xen/mmu.c
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@ -57,8 +57,17 @@
#include "mmu.h"
#define P2M_ENTRIES_PER_PAGE (PAGE_SIZE / sizeof(unsigned long))
#define TOP_ENTRIES (MAX_DOMAIN_PAGES / P2M_ENTRIES_PER_PAGE)
static unsigned long *p2m_top[MAX_DOMAIN_PAGES / P2M_ENTRIES_PER_PAGE];
/* Placeholder for holes in the address space */
static unsigned long p2m_missing[P2M_ENTRIES_PER_PAGE]
__attribute__((section(".data.page_aligned"))) =
{ [ 0 ... P2M_ENTRIES_PER_PAGE-1 ] = ~0UL };
/* Array of pointers to pages containing p2m entries */
static unsigned long *p2m_top[TOP_ENTRIES]
__attribute__((section(".data.page_aligned"))) =
{ [ 0 ... TOP_ENTRIES - 1] = &p2m_missing[0] };
static inline unsigned p2m_top_index(unsigned long pfn)
{
@ -92,9 +101,6 @@ unsigned long get_phys_to_machine(unsigned long pfn)
return INVALID_P2M_ENTRY;
topidx = p2m_top_index(pfn);
if (p2m_top[topidx] == NULL)
return INVALID_P2M_ENTRY;
idx = p2m_index(pfn);
return p2m_top[topidx][idx];
}
@ -110,7 +116,7 @@ static void alloc_p2m(unsigned long **pp)
for(i = 0; i < P2M_ENTRIES_PER_PAGE; i++)
p[i] = INVALID_P2M_ENTRY;
if (cmpxchg(pp, NULL, p) != NULL)
if (cmpxchg(pp, p2m_missing, p) != p2m_missing)
free_page((unsigned long)p);
}
@ -129,7 +135,7 @@ void set_phys_to_machine(unsigned long pfn, unsigned long mfn)
}
topidx = p2m_top_index(pfn);
if (p2m_top[topidx] == NULL) {
if (p2m_top[topidx] == p2m_missing) {
/* no need to allocate a page to store an invalid entry */
if (mfn == INVALID_P2M_ENTRY)
return;