#include <asm/thread_info.h>
#include <asm/processor-flags.h>
-/*G:020 Our story starts with the kernel booting into startup_32 in
+/*G:020
+ * Our story starts with the kernel booting into startup_32 in
* arch/x86/kernel/head_32.S. It expects a boot header, which is created by
* the bootloader (the Launcher in our case).
*
* data without remembering to subtract __PAGE_OFFSET!
*
* The .section line puts this code in .init.text so it will be discarded after
- * boot. */
+ * boot.
+ */
.section .init.text, "ax", @progbits
ENTRY(lguest_entry)
- /* 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 about
+ * us, and also find out where it put our page tables.
+ */
movl $LHCALL_LGUEST_INIT, %eax
movl $lguest_data - __PAGE_OFFSET, %ebx
.byte 0x0f,0x01,0xc1 /* KVM_HYPERCALL */
/* Set up the initial stack so we can run C code. */
movl $(init_thread_union+THREAD_SIZE),%esp
- /* Jumps are relative, and we're running __PAGE_OFFSET too low at the
- * moment. */
+ /* Jumps are relative: we're running __PAGE_OFFSET too low. */
jmp lguest_init+__PAGE_OFFSET
-/*G:055 We create a macro which puts the assembler code between lgstart_ and
- * lgend_ markers. These templates are put in the .text section: they can't be
- * discarded after boot as we may need to patch modules, too. */
+/*G:055
+ * We create a macro which puts the assembler code between lgstart_ and lgend_
+ * markers. These templates are put in the .text section: they can't be
+ * discarded after boot as we may need to patch modules, too.
+ */
.text
#define LGUEST_PATCH(name, insns...) \
lgstart_##name: insns; lgend_##name:; \
LGUEST_PATCH(cli, movl $0, lguest_data+LGUEST_DATA_irq_enabled)
LGUEST_PATCH(pushf, movl lguest_data+LGUEST_DATA_irq_enabled, %eax)
-/*G:033 But using those wrappers is inefficient (we'll see why that doesn't
- * matter for save_fl and irq_disable later). If we write our routines
- * carefully in assembler, we can avoid clobbering any registers and avoid
- * jumping through the wrapper functions.
+/*G:033
+ * But using those wrappers is inefficient (we'll see why that doesn't matter
+ * for save_fl and irq_disable later). If we write our routines carefully in
+ * assembler, we can avoid clobbering any registers and avoid jumping through
+ * the wrapper functions.
*
* I skipped over our first piece of assembler, but this one is worth studying
- * in a bit more detail so I'll describe in easy stages. First, the routine
- * to enable interrupts: */
+ * in a bit more detail so I'll describe in easy stages. First, the routine to
+ * enable interrupts:
+ */
ENTRY(lg_irq_enable)
- /* The reverse of irq_disable, this sets lguest_data.irq_enabled to
- * X86_EFLAGS_IF (ie. "Interrupts enabled"). */
+ /*
+ * The reverse of irq_disable, this sets lguest_data.irq_enabled to
+ * X86_EFLAGS_IF (ie. "Interrupts enabled").
+ */
movl $X86_EFLAGS_IF, lguest_data+LGUEST_DATA_irq_enabled
- /* But now we need to check if the Host wants to know: there might have
+ /*
+ * But now we need to check if the Host wants to know: there might have
* been interrupts waiting to be delivered, in which case it will have
* set lguest_data.irq_pending to X86_EFLAGS_IF. If it's not zero, we
- * jump to send_interrupts, otherwise we're done. */
+ * jump to send_interrupts, otherwise we're done.
+ */
testl $0, lguest_data+LGUEST_DATA_irq_pending
jnz send_interrupts
- /* One cool thing about x86 is that you can do many things without using
+ /*
+ * One cool thing about x86 is that you can do many things without using
* a register. In this case, the normal path hasn't needed to save or
- * restore any registers at all! */
+ * restore any registers at all!
+ */
ret
send_interrupts:
- /* OK, now we need a register: eax is used for the hypercall number,
+ /*
+ * OK, now we need a register: eax is used for the hypercall number,
* which is LHCALL_SEND_INTERRUPTS.
*
* We used not to bother with this pending detection at all, which was
* much simpler. Sooner or later the Host would realize it had to
* send us an interrupt. But that turns out to make performance 7
* times worse on a simple tcp benchmark. So now we do this the hard
- * way. */
+ * way.
+ */
pushl %eax
movl $LHCALL_SEND_INTERRUPTS, %eax
- /* This is a vmcall instruction (same thing that KVM uses). Older
+ /*
+ * This is a vmcall instruction (same thing that KVM uses). Older
* assembler versions might not know the "vmcall" instruction, so we
- * create one manually here. */
+ * create one manually here.
+ */
.byte 0x0f,0x01,0xc1 /* KVM_HYPERCALL */
+ /* Put eax back the way we found it. */
popl %eax
ret
-/* Finally, the "popf" or "restore flags" routine. The %eax register holds the
+/*
+ * Finally, the "popf" or "restore flags" routine. The %eax register holds the
* flags (in practice, either X86_EFLAGS_IF or 0): if it's X86_EFLAGS_IF we're
- * enabling interrupts again, if it's 0 we're leaving them off. */
+ * enabling interrupts again, if it's 0 we're leaving them off.
+ */
ENTRY(lg_restore_fl)
/* This is just "lguest_data.irq_enabled = flags;" */
movl %eax, lguest_data+LGUEST_DATA_irq_enabled
- /* Now, if the %eax value has enabled interrupts and
+ /*
+ * Now, if the %eax value has enabled interrupts and
* lguest_data.irq_pending is set, we want to tell the Host so it can
* deliver any outstanding interrupts. Fortunately, both values will
* be X86_EFLAGS_IF (ie. 512) in that case, and the "testl"
* instruction will AND them together for us. If both are set, we
- * jump to send_interrupts. */
+ * jump to send_interrupts.
+ */
testl lguest_data+LGUEST_DATA_irq_pending, %eax
jnz send_interrupts
/* Again, the normal path has used no extra registers. Clever, huh? */
ret
+/*:*/
/* These demark the EIP range where host should never deliver interrupts. */
.global lguest_noirq_start
.global lguest_noirq_end
-/*M:004 When the Host reflects a trap or injects an interrupt into the Guest,
- * it sets the eflags interrupt bit on the stack based on
- * lguest_data.irq_enabled, so the Guest iret logic does the right thing when
- * restoring it. However, when the Host sets the Guest up for direct traps,
- * such as system calls, the processor is the one to push eflags onto the
- * stack, and the interrupt bit will be 1 (in reality, interrupts are always
- * enabled in the Guest).
+/*M:004
+ * When the Host reflects a trap or injects an interrupt into the Guest, it
+ * sets the eflags interrupt bit on the stack based on lguest_data.irq_enabled,
+ * so the Guest iret logic does the right thing when restoring it. However,
+ * when the Host sets the Guest up for direct traps, such as system calls, the
+ * processor is the one to push eflags onto the stack, and the interrupt bit
+ * will be 1 (in reality, interrupts are always enabled in the Guest).
*
* This turns out to be harmless: the only trap which should happen under Linux
* with interrupts disabled is Page Fault (due to our lazy mapping of vmalloc
* regions), which has to be reflected through the Host anyway. If another
* trap *does* go off when interrupts are disabled, the Guest will panic, and
- * we'll never get to this iret! :*/
+ * we'll never get to this iret!
+:*/
-/*G:045 There is one final paravirt_op that the Guest implements, and glancing
- * at it you can see why I left it to last. It's *cool*! It's in *assembler*!
+/*G:045
+ * There is one final paravirt_op that the Guest implements, and glancing at it
+ * you can see why I left it to last. It's *cool*! It's in *assembler*!
*
* The "iret" instruction is used to return from an interrupt or trap. The
* stack looks like this:
* return to userspace or wherever. Our solution to this is to surround the
* code with lguest_noirq_start: and lguest_noirq_end: labels. We tell the
* Host that it is *never* to interrupt us there, even if interrupts seem to be
- * enabled. */
+ * enabled.
+ */
ENTRY(lguest_iret)
pushl %eax
movl 12(%esp), %eax
lguest_noirq_start:
- /* Note the %ss: segment prefix here. Normal data accesses use the
+ /*
+ * Note the %ss: segment prefix here. Normal data accesses use the
* "ds" segment, but that will have already been restored for whatever
* we're returning to (such as userspace): we can't trust it. The %ss:
- * prefix makes sure we use the stack segment, which is still valid. */
+ * prefix makes sure we use the stack segment, which is still valid.
+ */
movl %eax,%ss:lguest_data+LGUEST_DATA_irq_enabled
popl %eax
iret
git.openpandora.org / pandora-kernel.git / blobdiff