From 61c6dfce3296da2643c4c4f90eaab6fa3c1cf8b3 Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Thu, 13 Jun 2013 10:49:01 +0200 Subject: [PATCH] x86: fix map_domain_page() last resort fallback Guests with vCPU count not divisible by 4 have unused bits in the last word of their inuse bitmap, and the garbage collection code therefore would get mislead believing that some entries were actually recoverable for use. Also use an earlier established local variable in mapcache_vcpu_init() instead of re-calculating the value (noticed while investigating the generally better option of setting those overhanging bits once during setup - this didn't work out in a simple enough fashion because the mapping getting established there isn't in the current address space, and hence the bitmap isn't directly accessible there). Reported-by: Konrad Wilk Signed-off-by: Jan Beulich Acked-by: Keir Fraser --- xen/arch/x86/domain_page.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/xen/arch/x86/domain_page.c b/xen/arch/x86/domain_page.c index efda6afd8b..9297ea07e6 100644 --- a/xen/arch/x86/domain_page.c +++ b/xen/arch/x86/domain_page.c @@ -110,16 +110,17 @@ void *map_domain_page(unsigned long mfn) idx = find_next_zero_bit(dcache->inuse, dcache->entries, dcache->cursor); if ( unlikely(idx >= dcache->entries) ) { - unsigned long accum = 0; + unsigned long accum = 0, prev = 0; /* /First/, clean the garbage map and update the inuse list. */ for ( i = 0; i < BITS_TO_LONGS(dcache->entries); i++ ) { + accum |= prev; dcache->inuse[i] &= ~xchg(&dcache->garbage[i], 0); - accum |= ~dcache->inuse[i]; + prev = ~dcache->inuse[i]; } - if ( accum ) + if ( accum | (prev & BITMAP_LAST_WORD_MASK(dcache->entries)) ) idx = find_first_zero_bit(dcache->inuse, dcache->entries); else { @@ -279,8 +280,7 @@ int mapcache_vcpu_init(struct vcpu *v) if ( ents > dcache->entries ) { /* Populate page tables. */ - int rc = create_perdomain_mapping(d, MAPCACHE_VIRT_START, - d->max_vcpus * MAPCACHE_VCPU_ENTRIES, + int rc = create_perdomain_mapping(d, MAPCACHE_VIRT_START, ents, NIL(l1_pgentry_t *), NULL); /* Populate bit maps. */ -- 2.39.5