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: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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@ -57,8 +57,17 @@
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#include "mmu.h"
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#define P2M_ENTRIES_PER_PAGE (PAGE_SIZE / sizeof(unsigned long))
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#define TOP_ENTRIES (MAX_DOMAIN_PAGES / P2M_ENTRIES_PER_PAGE)
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static unsigned long *p2m_top[MAX_DOMAIN_PAGES / P2M_ENTRIES_PER_PAGE];
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/* Placeholder for holes in the address space */
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static unsigned long p2m_missing[P2M_ENTRIES_PER_PAGE]
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__attribute__((section(".data.page_aligned"))) =
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{ [ 0 ... P2M_ENTRIES_PER_PAGE-1 ] = ~0UL };
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/* Array of pointers to pages containing p2m entries */
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static unsigned long *p2m_top[TOP_ENTRIES]
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__attribute__((section(".data.page_aligned"))) =
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{ [ 0 ... TOP_ENTRIES - 1] = &p2m_missing[0] };
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static inline unsigned p2m_top_index(unsigned long pfn)
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{
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@ -92,9 +101,6 @@ unsigned long get_phys_to_machine(unsigned long pfn)
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return INVALID_P2M_ENTRY;
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topidx = p2m_top_index(pfn);
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if (p2m_top[topidx] == NULL)
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return INVALID_P2M_ENTRY;
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idx = p2m_index(pfn);
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return p2m_top[topidx][idx];
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}
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@ -110,7 +116,7 @@ static void alloc_p2m(unsigned long **pp)
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for(i = 0; i < P2M_ENTRIES_PER_PAGE; i++)
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p[i] = INVALID_P2M_ENTRY;
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if (cmpxchg(pp, NULL, p) != NULL)
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if (cmpxchg(pp, p2m_missing, p) != p2m_missing)
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free_page((unsigned long)p);
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}
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@ -129,7 +135,7 @@ void set_phys_to_machine(unsigned long pfn, unsigned long mfn)
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}
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topidx = p2m_top_index(pfn);
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if (p2m_top[topidx] == NULL) {
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if (p2m_top[topidx] == p2m_missing) {
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/* no need to allocate a page to store an invalid entry */
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if (mfn == INVALID_P2M_ENTRY)
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return;
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