path: root/arch/x86/lguest
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authorRusty Russell <rusty@rustcorp.com.au>2011-07-22 14:39:48 +0930
committerRusty Russell <rusty@rustcorp.com.au>2011-07-22 14:39:48 +0930
commit5dea1c88ed11a1221581c4b202f053c4fc138704 (patch)
tree59e15d3c696712e26ffb229ff987f33bcc72affe /arch/x86/lguest
parente0377e25206328998d036cafddcd00a7c3252e3e (diff)
lguest: use a special 1:1 linear pagetable mode until first switch.
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>
Diffstat (limited to 'arch/x86/lguest')
2 files changed, 12 insertions, 8 deletions
diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
index db832fd65ecb..719a32c60516 100644
--- a/arch/x86/lguest/boot.c
+++ b/arch/x86/lguest/boot.c
@@ -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);
diff --git a/arch/x86/lguest/i386_head.S b/arch/x86/lguest/i386_head.S
index 4f420c2f2d55..863b03a9fbff 100644
--- a/arch/x86/lguest/i386_head.S
+++ b/arch/x86/lguest/i386_head.S
@@ -27,13 +27,18 @@
.section .init.text, "ax", @progbits
- * We make the "initialization" hypercall now to tell the Host about
- * us, and also find out where it put our page tables.
+ * We make the "initialization" hypercall now to tell the Host where
+ * our lguest_data struct is.
movl $lguest_data - __PAGE_OFFSET, %ebx
+ /* Now turn our pagetables on; setup by arch/x86/kernel/head_32.S. */
+ movl $LHCALL_NEW_PGTABLE, %eax
+ movl $(initial_page_table - __PAGE_OFFSET), %ebx
/* Set up the initial stack so we can run C code. */
movl $(init_thread_union+THREAD_SIZE),%esp

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