diff options
Diffstat (limited to 'drivers/lguest/lg.h')
| -rw-r--r-- | drivers/lguest/lg.h | 19 |
1 files changed, 16 insertions, 3 deletions
diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h index 3b9dc123a7df..269116eee85f 100644 --- a/drivers/lguest/lg.h +++ b/drivers/lguest/lg.h @@ -58,9 +58,18 @@ struct lguest_dma_info u8 interrupt; /* 0 when not registered */ }; -/* We have separate types for the guest's ptes & pgds and the shadow ptes & - * pgds. Since this host might use three-level pagetables and the guest and - * shadow pagetables don't, we can't use the normal pte_t/pgd_t. */ +/*H:310 The page-table code owes a great debt of gratitude to Andi Kleen. He + * reviewed the original code which used "u32" for all page table entries, and + * insisted that it would be far clearer with explicit typing. I thought it + * was overkill, but he was right: it is much clearer than it was before. + * + * We have separate types for the Guest's ptes & pgds and the shadow ptes & + * pgds. There's already a Linux type for these (pte_t and pgd_t) but they + * change depending on kernel config options (PAE). */ + +/* Each entry is identical: lower 12 bits of flags and upper 20 bits for the + * "page frame number" (0 == first physical page, etc). They are different + * types so the compiler will warn us if we mix them improperly. */ typedef union { struct { unsigned flags:12, pfn:20; }; struct { unsigned long val; } raw; @@ -77,8 +86,12 @@ typedef union { struct { unsigned flags:12, pfn:20; }; struct { unsigned long val; } raw; } gpte_t; + +/* We have two convenient macros to convert a "raw" value as handed to us by + * the Guest into the correct Guest PGD or PTE type. */ #define mkgpte(_val) ((gpte_t){.raw.val = _val}) #define mkgpgd(_val) ((gpgd_t){.raw.val = _val}) +/*:*/ struct pgdir { |
