#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
* begin.
*/
-/* Is the descriptor the Guest wants us to put in OK?
- *
- * The flag which Intel says must be zero: must be zero. The descriptor must
- * be present, (this is actually checked earlier but is here for thorougness),
- * and the descriptor type must be 1 (a memory segment). */
-static int desc_ok(const struct desc_struct *gdt)
-{
- return ((gdt->b & 0x00209000) == 0x00009000);
-}
-
-/* Is the segment present? (Otherwise it can't be used by the Guest). */
-static int segment_present(const struct desc_struct *gdt)
-{
- return gdt->b & 0x8000;
-}
-
/* There are several entries we don't let the Guest set. The TSS entry is the
* "Task State Segment" which controls all kinds of delicate things. The
* LGUEST_CS and LGUEST_DS entries are reserved for the Switcher, and the
|| num == GDT_ENTRY_DOUBLEFAULT_TSS);
}
-/* If the Guest asks us to remove an entry from the GDT, we have to be careful.
- * If one of the segment registers is pointing at that entry the Switcher will
- * crash when it tries to reload the segment registers for the Guest.
- *
- * It doesn't make much sense for the Guest to try to remove its own code, data
- * or stack segments while they're in use: assume that's a Guest bug. If it's
- * one of the lesser segment registers using the removed entry, we simply set
- * that register to 0 (unusable). */
-static void check_segment_use(struct lguest *lg, unsigned int desc)
-{
- /* GDT entries are 8 bytes long, so we divide to get the index and
- * ignore the bottom bits. */
- if (lg->regs->gs / 8 == desc)
- lg->regs->gs = 0;
- if (lg->regs->fs / 8 == desc)
- lg->regs->fs = 0;
- if (lg->regs->es / 8 == desc)
- lg->regs->es = 0;
- if (lg->regs->ds / 8 == desc
- || lg->regs->cs / 8 == desc
- || lg->regs->ss / 8 == desc)
- kill_guest(lg, "Removed live GDT entry %u", desc);
-}
-/*:*/
-/*M:009 We wouldn't need to check for removal of in-use segments if we handled
- * faults in the Switcher. However, it's probably not a worthwhile
- * optimization. :*/
-
-/*H:610 Once the GDT has been changed, we look through the changed entries and
- * see if they're OK. If not, we'll call kill_guest() and the Guest will never
- * get to use the invalid entries. */
-static void fixup_gdt_table(struct lguest *lg, unsigned start, unsigned end)
+/*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
+ * mess: the message will be "unhandled trap 256". */
+static void fixup_gdt_table(struct lg_cpu *cpu, unsigned start, unsigned end)
{
unsigned int i;
if (ignored_gdt(i))
continue;
- /* We could fault in switch_to_guest if they are using
- * a removed segment. */
- if (!segment_present(&lg->gdt[i])) {
- check_segment_use(lg, i);
- continue;
- }
-
- if (!desc_ok(&lg->gdt[i]))
- kill_guest(lg, "Bad GDT descriptor %i", i);
-
/* Segment descriptors contain a privilege level: the Guest is
* sometimes careless and leaves this as 0, even though it's
* running at privilege level 1. If so, we fix it here. */
- if ((lg->gdt[i].b & 0x00006000) == 0)
- lg->gdt[i].b |= (GUEST_PL << 13);
+ if ((cpu->arch.gdt[i].b & 0x00006000) == 0)
+ cpu->arch.gdt[i].b |= (GUEST_PL << 13);
/* Each descriptor has an "accessed" bit. If we don't set it
* now, the CPU will try to set it when the Guest first loads
* that entry into a segment register. But the GDT isn't
* writable by the Guest, so bad things can happen. */
- lg->gdt[i].b |= 0x00000100;
+ cpu->arch.gdt[i].b |= 0x00000100;
}
}
-/* 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. */
-void setup_guest_gdt(struct lguest *lg)
+/* This routine sets up the initial Guest GDT for booting. All entries start
+ * as 0 (unusable). */
+void setup_guest_gdt(struct lg_cpu *cpu)
{
/* Start with full 0-4G segments... */
- lg->gdt[GDT_ENTRY_KERNEL_CS] = FULL_EXEC_SEGMENT;
- lg->gdt[GDT_ENTRY_KERNEL_DS] = FULL_SEGMENT;
+ cpu->arch.gdt[GDT_ENTRY_KERNEL_CS] = FULL_EXEC_SEGMENT;
+ cpu->arch.gdt[GDT_ENTRY_KERNEL_DS] = FULL_SEGMENT;
/* ...except the Guest is allowed to use them, so set the privilege
* level appropriately in the flags. */
- lg->gdt[GDT_ENTRY_KERNEL_CS].b |= (GUEST_PL << 13);
- lg->gdt[GDT_ENTRY_KERNEL_DS].b |= (GUEST_PL << 13);
+ cpu->arch.gdt[GDT_ENTRY_KERNEL_CS].b |= (GUEST_PL << 13);
+ cpu->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. */
-void copy_gdt_tls(const struct lguest *lg, struct desc_struct *gdt)
+/*H:650 An optimization of copy_gdt(), for just the three "thead-local storage"
+ * entries. */
+void copy_gdt_tls(const struct lg_cpu *cpu, struct desc_struct *gdt)
{
unsigned int i;
for (i = GDT_ENTRY_TLS_MIN; i <= GDT_ENTRY_TLS_MAX; i++)
- gdt[i] = lg->gdt[i];
+ gdt[i] = cpu->arch.gdt[i];
}
-/* This is the full version */
-void copy_gdt(const struct lguest *lg, struct desc_struct *gdt)
+/*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 lg_cpu *cpu, struct desc_struct *gdt)
{
unsigned int i;
* replaced. See ignored_gdt() above. */
for (i = 0; i < GDT_ENTRIES; i++)
if (!ignored_gdt(i))
- gdt[i] = lg->gdt[i];
+ gdt[i] = cpu->arch.gdt[i];
}
-/* This is where the Guest asks us to load a new GDT (LHCALL_LOAD_GDT). */
-void load_guest_gdt(struct lguest *lg, unsigned long table, u32 num)
+/*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 lg_cpu *cpu, unsigned long table, u32 num)
{
/* We assume the Guest has the same number of GDT entries as the
* Host, otherwise we'd have to dynamically allocate the Guest GDT. */
- if (num > ARRAY_SIZE(lg->gdt))
- kill_guest(lg, "too many gdt entries %i", num);
+ if (num > ARRAY_SIZE(cpu->arch.gdt))
+ kill_guest(cpu, "too many gdt entries %i", num);
/* We read the whole thing in, then fix it up. */
- lgread(lg, lg->gdt, table, num * sizeof(lg->gdt[0]));
- fixup_gdt_table(lg, 0, ARRAY_SIZE(lg->gdt));
+ __lgread(cpu, cpu->arch.gdt, table, num * sizeof(cpu->arch.gdt[0]));
+ fixup_gdt_table(cpu, 0, ARRAY_SIZE(cpu->arch.gdt));
/* Mark that the GDT changed so the core knows it has to copy it again,
* even if the Guest is run on the same CPU. */
- lg->changed |= CHANGED_GDT;
+ cpu->changed |= CHANGED_GDT;
}
-void guest_load_tls(struct lguest *lg, unsigned long gtls)
+/* 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 lg_cpu *cpu, unsigned long gtls)
{
- struct desc_struct *tls = &lg->gdt[GDT_ENTRY_TLS_MIN];
+ struct desc_struct *tls = &cpu->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);
- lg->changed |= CHANGED_GDT_TLS;
+ __lgread(cpu, tls, gtls, sizeof(*tls)*GDT_ENTRY_TLS_ENTRIES);
+ fixup_gdt_table(cpu, GDT_ENTRY_TLS_MIN, GDT_ENTRY_TLS_MAX+1);
+ /* Note that just the TLS entries have changed. */
+ cpu->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
git.openpandora.org / pandora-kernel.git / blobdiff