-/*P:600 The x86 architecture has segments, which involve a table of descriptors
+/*P:600
+ * The x86 architecture has segments, which involve a table of descriptors
* which can be used to do funky things with virtual address interpretation.
* We originally used to use segments so the Guest couldn't alter the
* Guest<->Host Switcher, and then we had to trim Guest segments, and restore
*
* In these modern times, the segment handling code consists of simple sanity
* checks, and the worst you'll experience reading this code is butterfly-rash
- * from frolicking through its parklike serenity. :*/
+ * from frolicking through its parklike serenity.
+:*/
#include "lg.h"
/*H:600
* begin.
*/
-/* There are several entries we don't let the Guest set. The TSS entry is the
+/*
+ * 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
- * the Guest can't be trusted to deal with double faults. */
+ * the Guest can't be trusted to deal with double faults.
+ */
static bool ignored_gdt(unsigned int num)
{
return (num == GDT_ENTRY_TSS
|| num == GDT_ENTRY_DOUBLEFAULT_TSS);
}
-/*H:630 Once the Guest gave us new GDT entries, we fix them 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
- * mess: the message will be "unhandled trap 256". */
+ * mess: the message will be "unhandled trap 256".
+ */
static void fixup_gdt_table(struct lg_cpu *cpu, unsigned start, unsigned end)
{
unsigned int i;
for (i = start; i < end; i++) {
- /* We never copy these ones to real GDT, so we don't care what
- * they say */
+ /*
+ * We never copy these ones to real GDT, so we don't care what
+ * they say
+ */
if (ignored_gdt(i))
continue;
- /* Segment descriptors contain a privilege level: the Guest is
+ /*
+ * 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. */
+ * running at privilege level 1. If so, we fix it here.
+ */
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
+ /*
+ * 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. */
+ * writable by the Guest, so bad things can happen.
+ */
cpu->arch.gdt[i].b |= 0x00000100;
}
}
-/*H:610 Like the IDT, we never simply use the GDT the Guest gives us. We keep
+/*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. */
+ * running.
+ */
void setup_default_gdt_entries(struct lguest_ro_state *state)
{
struct desc_struct *gdt = state->guest_gdt;
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 particular CPU.
+ /*
+ * 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. */
+ * 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 sets up the initial Guest GDT for booting. All entries start
- * as 0 (unusable). */
+/*
+ * 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... */
+ /*
+ * Start with full 0-4G segments...except the Guest is allowed to use
+ * them, so set the privilege level appropriately in the flags.
+ */
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. */
cpu->arch.gdt[GDT_ENTRY_KERNEL_CS].b |= (GUEST_PL << 13);
cpu->arch.gdt[GDT_ENTRY_KERNEL_DS].b |= (GUEST_PL << 13);
}
-/*H:650 An optimization of copy_gdt(), for just the three "thead-local storage"
- * entries. */
+/*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;
gdt[i] = cpu->arch.gdt[i];
}
-/*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. */
+/*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;
- /* The default entries from setup_default_gdt_entries() are not
- * replaced. See ignored_gdt() above. */
+ /*
+ * The default entries from setup_default_gdt_entries() are not
+ * replaced. See ignored_gdt() above.
+ */
for (i = 0; i < GDT_ENTRIES; i++)
if (!ignored_gdt(i))
gdt[i] = cpu->arch.gdt[i];
}
-/*H:620 This is where the Guest asks us to load a new GDT entry
- * (LHCALL_LOAD_GDT_ENTRY). We tweak the entry and copy it in. */
+/*H:620
+ * This is where the Guest asks us to load a new GDT entry
+ * (LHCALL_LOAD_GDT_ENTRY). We tweak the entry and copy it in.
+ */
void load_guest_gdt_entry(struct lg_cpu *cpu, u32 num, u32 lo, u32 hi)
{
- /* We assume the Guest has the same number of GDT entries as the
- * Host, otherwise we'd have to dynamically allocate the Guest GDT. */
+ /*
+ * 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(cpu->arch.gdt))
kill_guest(cpu, "too many gdt entries %i", num);
cpu->arch.gdt[num].a = lo;
cpu->arch.gdt[num].b = hi;
fixup_gdt_table(cpu, num, num+1);
- /* 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. */
+ /*
+ * 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.
+ */
cpu->changed |= CHANGED_GDT;
}
-/* This is the fast-track version for just changing the three TLS entries.
+/*
+ * 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? */
+ * both cases?
+ */
void guest_load_tls(struct lg_cpu *cpu, unsigned long gtls)
{
struct desc_struct *tls = &cpu->arch.gdt[GDT_ENTRY_TLS_MIN];
/* Note that just the TLS entries have changed. */
cpu->changed |= CHANGED_GDT_TLS;
}
-/*:*/
/*H:660
* With this, we have finished the Host.
git.openpandora.org / pandora-kernel.git / blobdiff