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lguest: comment documentation update.

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Took some cycles to re-read the Lguest Journey end-to-end, fix some
rot and tighten some phrases.

Only comments change.  No new jokes, but a couple of recycled old jokes.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell
2008-03-28 11:05:53 -05:00
parent e18b094f0f
commit a6bd8e1303
13 changed files with 208 additions and 142 deletions
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32
drivers/lguest/page_tables.c
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@@ -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. */