diff options
Diffstat (limited to 'drivers/lguest/page_tables.c')
| -rw-r--r-- | drivers/lguest/page_tables.c | 32 |
1 files changed, 18 insertions, 14 deletions
diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c index a7f64a9d67e0..d93500f24fbb 100644 --- a/drivers/lguest/page_tables.c +++ b/drivers/lguest/page_tables.c @@ -2,8 +2,8 @@ * previous encounters. It's functional, and as neat as it can be in the * circumstances, but be wary, for these things are subtle and break easily. * The Guest provides a virtual to physical mapping, but we can neither trust - * it nor use it: we verify and convert it here to point the hardware to the - * actual Guest pages when running the Guest. :*/ + * it nor use it: we verify and convert it here then point the CPU to the + * converted Guest pages when running the Guest. :*/ /* Copyright (C) Rusty Russell IBM Corporation 2006. * GPL v2 and any later version */ @@ -106,6 +106,11 @@ static unsigned long gpte_addr(pgd_t gpgd, unsigned long vaddr) BUG_ON(!(pgd_flags(gpgd) & _PAGE_PRESENT)); return gpage + ((vaddr>>PAGE_SHIFT) % PTRS_PER_PTE) * sizeof(pte_t); } +/*:*/ + +/*M:014 get_pfn is slow; it takes the mmap sem and calls get_user_pages. We + * could probably try to grab batches of pages here as an optimization + * (ie. pre-faulting). :*/ /*H:350 This routine takes a page number given by the Guest and converts it to * an actual, physical page number. It can fail for several reasons: the @@ -113,8 +118,8 @@ static unsigned long gpte_addr(pgd_t gpgd, unsigned long vaddr) * and the page is read-only, or the write flag was set and the page was * shared so had to be copied, but we ran out of memory. * - * This holds a reference to the page, so release_pte() is careful to - * put that back. */ + * This holds a reference to the page, so release_pte() is careful to put that + * back. */ static unsigned long get_pfn(unsigned long virtpfn, int write) { struct page *page; @@ -532,13 +537,13 @@ static void do_set_pte(struct lg_cpu *cpu, int idx, * all processes. So when the page table above that address changes, we update * all the page tables, not just the current one. This is rare. * - * The benefit is that when we have to track a new page table, we can copy keep - * all the kernel mappings. This speeds up context switch immensely. */ + * The benefit is that when we have to track a new page table, we can keep all + * the kernel mappings. This speeds up context switch immensely. */ void guest_set_pte(struct lg_cpu *cpu, unsigned long gpgdir, unsigned long vaddr, pte_t gpte) { - /* Kernel mappings must be changed on all top levels. Slow, but - * doesn't happen often. */ + /* Kernel mappings must be changed on all top levels. Slow, but doesn't + * happen often. */ if (vaddr >= cpu->lg->kernel_address) { unsigned int i; for (i = 0; i < ARRAY_SIZE(cpu->lg->pgdirs); i++) @@ -704,12 +709,11 @@ static __init void populate_switcher_pte_page(unsigned int cpu, /* We've made it through the page table code. Perhaps our tired brains are * still processing the details, or perhaps we're simply glad it's over. * - * If nothing else, note that all this complexity in juggling shadow page - * tables in sync with the Guest's page tables is for one reason: for most - * Guests this page table dance determines how bad performance will be. This - * is why Xen uses exotic direct Guest pagetable manipulation, and why both - * Intel and AMD have implemented shadow page table support directly into - * hardware. + * If nothing else, note that all this complexity in juggling shadow page tables + * in sync with the Guest's page tables is for one reason: for most Guests this + * page table dance determines how bad performance will be. This is why Xen + * uses exotic direct Guest pagetable manipulation, and why both Intel and AMD + * have implemented shadow page table support directly into hardware. * * There is just one file remaining in the Host. */ |