Commit cf0923ea authored by Jeremy Fitzhardinge's avatar Jeremy Fitzhardinge Committed by Thomas Gleixner
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xen: efficiently support a holey p2m table 



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: default avatarJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 8006ec3e

arch/x86/xen/mmu.c

+12 −6
Original line number Diff line number Diff line
@@ -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;

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