[PATCH] paravirt: Patch inline replacements for paravirt intercepts

It turns out that the most called ops, by several orders of magnitude,
are the interrupt manipulation ops.  These are obvious candidates for
patching, so mark them up and create infrastructure for it.

The method used is that the ops structure has a patch function, which
is called for each place which needs to be patched: this returns a
number of instructions (the rest are NOP-padded).

Usually we can spare a register (%eax) for the binary patched code to
use, but in a couple of critical places in entry.S we can't: we make
the clobbers explicit at the call site, and manually clobber the
allowed registers in debug mode as an extra check.

And:

Don't abuse CONFIG_DEBUG_KERNEL, add CONFIG_DEBUG_PARAVIRT.

And:

AK:  Fix warnings in x86-64 alternative.c build

And:

AK: Fix compilation with defconfig

And:

^From: Andrew Morton <akpm@osdl.org>

Some binutlises still like to emit references to __stop_parainstructions and
__start_parainstructions.

And:

AK: Fix warnings about unused variables when PARAVIRT is disabled.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Zachary Amsden <zach@vmware.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>

1 files changed, 44 insertions, 0 deletions

diff --git a/arch/i386/kernel/paravirt.c b/arch/i386/kernel/paravirt.c
index 478192cd4b90..d46460426446 100644
--- a/arch/i386/kernel/paravirt.c
+++ b/arch/i386/kernel/paravirt.c
@@ -45,6 +45,49 @@ char *memory_setup(void)
         return paravirt_ops.memory_setup();
 }
 
+/* Simple instruction patching code. */
+#define DEF_NATIVE(name, code)                                  \
+        extern const char start_##name[], end_##name[];         \
+        asm("start_" #name ": " code "; end_" #name ":")
+DEF_NATIVE(cli, "cli");
+DEF_NATIVE(sti, "sti");
+DEF_NATIVE(popf, "push %eax; popf");
+DEF_NATIVE(pushf, "pushf; pop %eax");
+DEF_NATIVE(pushf_cli, "pushf; pop %eax; cli");
+DEF_NATIVE(iret, "iret");
+DEF_NATIVE(sti_sysexit, "sti; sysexit");
+
+static const struct native_insns
+{
+        const char *start, *end;
+} native_insns[] = {
+        [PARAVIRT_IRQ_DISABLE] = { start_cli, end_cli },
+        [PARAVIRT_IRQ_ENABLE] = { start_sti, end_sti },
+        [PARAVIRT_RESTORE_FLAGS] = { start_popf, end_popf },
+        [PARAVIRT_SAVE_FLAGS] = { start_pushf, end_pushf },
+        [PARAVIRT_SAVE_FLAGS_IRQ_DISABLE] = { start_pushf_cli, end_pushf_cli },
+        [PARAVIRT_INTERRUPT_RETURN] = { start_iret, end_iret },
+        [PARAVIRT_STI_SYSEXIT] = { start_sti_sysexit, end_sti_sysexit },
+};
+
+static unsigned native_patch(u8 type, u16 clobbers, void *insns, unsigned len)
+{
+        unsigned int insn_len;
+
+        /* Don't touch it if we don't have a replacement */
+        if (type >= ARRAY_SIZE(native_insns) || !native_insns[type].start)
+                return len;
+
+        insn_len = native_insns[type].end - native_insns[type].start;
+
+        /* Similarly if we can't fit replacement. */
+        if (len < insn_len)
+                return len;
+
+        memcpy(insns, native_insns[type].start, insn_len);
+        return insn_len;
+}
+
 static fastcall unsigned long native_get_debugreg(int regno)
 {
         unsigned long val = 0;  /* Damn you, gcc! */
@@ -349,6 +392,7 @@ struct paravirt_ops paravirt_ops = {
         .paravirt_enabled = 0,
         .kernel_rpl = 0,
 
+        .patch = native_patch,
         .banner = default_banner,
         .arch_setup = native_nop,
         .memory_setup = machine_specific_memory_setup,