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lguest: use a special 1:1 linear pagetable mode until first switch.

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The Host used to create some page tables for the Guest to use at the
top of Guest memory; it would then tell the Guest where this was.  In
particular, it created linear mappings for 0 and 0xC0000000 addresses
because lguest used to switch to its real page tables quite late in
boot.

However, since d50d8fe19 Linux initialized boot page tables in
head_32.S even before the "are we lguest?" boot jump.  So, now we can
simplify things: the Host pagetable code assumes 1:1 linear mapping
until it first calls the LHCALL_NEW_PGTABLE hypercall, which we now do
before we reach C code.

This also means that the Host doesn't need to know anything about the
Guest's PAGE_OFFSET.  (Non-Linux guests might not even have such a
thing).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell
2011-07-22 14:39:48 +09:30
parent e0377e2520
commit 5dea1c88ed
6 changed files with 98 additions and 205 deletions
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11
arch/x86/lguest/boot.c
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@@ -520,17 +520,16 @@ static unsigned long lguest_read_cr2(void)
/* See lguest_set_pte() below. */
static bool cr3_changed = false;
static unsigned long current_cr3;
/*
* cr3 is the current toplevel pagetable page: the principle is the same as
* cr0. Keep a local copy, and tell the Host when it changes. The only
* difference is that our local copy is in lguest_data because the Host needs
* to set it upon our initial hypercall.
* cr0. Keep a local copy, and tell the Host when it changes.
*/
static void lguest_write_cr3(unsigned long cr3)
{
lguest_data.pgdir = cr3;
lazy_hcall1(LHCALL_NEW_PGTABLE, cr3);
current_cr3 = cr3;
/* These two page tables are simple, linear, and used during boot */
if (cr3 != __pa(swapper_pg_dir) && cr3 != __pa(initial_page_table))
@@ -539,7 +538,7 @@ static void lguest_write_cr3(unsigned long cr3)
static unsigned long lguest_read_cr3(void)
{
return lguest_data.pgdir;
return current_cr3;
}
/* cr4 is used to enable and disable PGE, but we don't care. */
@@ -758,7 +757,7 @@ static void lguest_pmd_clear(pmd_t *pmdp)
static void lguest_flush_tlb_single(unsigned long addr)
{
/* Simply set it to zero: if it was not, it will fault back in. */
lazy_hcall3(LHCALL_SET_PTE, lguest_data.pgdir, addr, 0);
lazy_hcall3(LHCALL_SET_PTE, current_cr3, addr, 0);
}
/*