diff options
Diffstat (limited to 'drivers/lguest/segments.c')
| -rw-r--r-- | drivers/lguest/segments.c | 48 |
1 files changed, 29 insertions, 19 deletions
diff --git a/drivers/lguest/segments.c b/drivers/lguest/segments.c index c2434ec99f7..9e189cbec7d 100644 --- a/drivers/lguest/segments.c +++ b/drivers/lguest/segments.c @@ -12,8 +12,6 @@ #include "lg.h" /*H:600 - * We've almost completed the Host; there's just one file to go! - * * Segments & The Global Descriptor Table * * (That title sounds like a bad Nerdcore group. Not to suggest that there are @@ -55,7 +53,7 @@ static int ignored_gdt(unsigned int num) || num == GDT_ENTRY_DOUBLEFAULT_TSS); } -/*H:610 Once the GDT has been changed, we fix the new entries up a little. We +/*H:630 Once the Guest gave us new GDT entries, we fix them up a little. We * don't care if they're invalid: the worst that can happen is a General * Protection Fault in the Switcher when it restores a Guest segment register * which tries to use that entry. Then we kill the Guest for causing such a @@ -84,25 +82,33 @@ static void fixup_gdt_table(struct lguest *lg, unsigned start, unsigned end) } } -/* This routine is called at boot or modprobe time for each CPU to set up the - * "constant" GDT entries for Guests running on that CPU. */ +/*H:610 Like the IDT, we never simply use the GDT the Guest gives us. We keep + * a GDT for each CPU, and copy across the Guest's entries each time we want to + * run the Guest on that CPU. + * + * This routine is called at boot or modprobe time for each CPU to set up the + * constant GDT entries: the ones which are the same no matter what Guest we're + * running. */ void setup_default_gdt_entries(struct lguest_ro_state *state) { struct desc_struct *gdt = state->guest_gdt; unsigned long tss = (unsigned long)&state->guest_tss; - /* The hypervisor segments are full 0-4G segments, privilege level 0 */ + /* The Switcher segments are full 0-4G segments, privilege level 0 */ gdt[GDT_ENTRY_LGUEST_CS] = FULL_EXEC_SEGMENT; gdt[GDT_ENTRY_LGUEST_DS] = FULL_SEGMENT; - /* The TSS segment refers to the TSS entry for this CPU, so we cannot - * copy it from the Guest. Forgive the magic flags */ + /* The TSS segment refers to the TSS entry for this particular CPU. + * Forgive the magic flags: the 0x8900 means the entry is Present, it's + * privilege level 0 Available 386 TSS system segment, and the 0x67 + * means Saturn is eclipsed by Mercury in the twelfth house. */ gdt[GDT_ENTRY_TSS].a = 0x00000067 | (tss << 16); gdt[GDT_ENTRY_TSS].b = 0x00008900 | (tss & 0xFF000000) | ((tss >> 16) & 0x000000FF); } -/* This routine is called before the Guest is run for the first time. */ +/* This routine sets up the initial Guest GDT for booting. All entries start + * as 0 (unusable). */ void setup_guest_gdt(struct lguest *lg) { /* Start with full 0-4G segments... */ @@ -114,13 +120,8 @@ void setup_guest_gdt(struct lguest *lg) lg->arch.gdt[GDT_ENTRY_KERNEL_DS].b |= (GUEST_PL << 13); } -/* Like the IDT, we never simply use the GDT the Guest gives us. We set up the - * GDTs for each CPU, then we copy across the entries each time we want to run - * a different Guest on that CPU. */ - -/* A partial GDT load, for the three "thead-local storage" entries. Otherwise - * it's just like load_guest_gdt(). So much, in fact, it would probably be - * neater to have a single hypercall to cover both. */ +/*H:650 An optimization of copy_gdt(), for just the three "thead-local storage" + * entries. */ void copy_gdt_tls(const struct lguest *lg, struct desc_struct *gdt) { unsigned int i; @@ -129,7 +130,9 @@ void copy_gdt_tls(const struct lguest *lg, struct desc_struct *gdt) gdt[i] = lg->arch.gdt[i]; } -/* This is the full version */ +/*H:640 When the Guest is run on a different CPU, or the GDT entries have + * changed, copy_gdt() is called to copy the Guest's GDT entries across to this + * CPU's GDT. */ void copy_gdt(const struct lguest *lg, struct desc_struct *gdt) { unsigned int i; @@ -141,7 +144,8 @@ void copy_gdt(const struct lguest *lg, struct desc_struct *gdt) gdt[i] = lg->arch.gdt[i]; } -/* This is where the Guest asks us to load a new GDT (LHCALL_LOAD_GDT). */ +/*H:620 This is where the Guest asks us to load a new GDT (LHCALL_LOAD_GDT). + * We copy it from the Guest and tweak the entries. */ void load_guest_gdt(struct lguest *lg, unsigned long table, u32 num) { /* We assume the Guest has the same number of GDT entries as the @@ -157,16 +161,22 @@ void load_guest_gdt(struct lguest *lg, unsigned long table, u32 num) lg->changed |= CHANGED_GDT; } +/* This is the fast-track version for just changing the three TLS entries. + * Remember that this happens on every context switch, so it's worth + * optimizing. But wouldn't it be neater to have a single hypercall to cover + * both cases? */ void guest_load_tls(struct lguest *lg, unsigned long gtls) { struct desc_struct *tls = &lg->arch.gdt[GDT_ENTRY_TLS_MIN]; __lgread(lg, tls, gtls, sizeof(*tls)*GDT_ENTRY_TLS_ENTRIES); fixup_gdt_table(lg, GDT_ENTRY_TLS_MIN, GDT_ENTRY_TLS_MAX+1); + /* Note that just the TLS entries have changed. */ lg->changed |= CHANGED_GDT_TLS; } +/*:*/ -/* +/*H:660 * With this, we have finished the Host. * * Five of the seven parts of our task are complete. You have made it through |