[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, 153 insertions, 36 deletions

diff --git a/include/asm-i386/paravirt.h b/include/asm-i386/paravirt.h
index a7551a44686f..081194751ade 100644
--- a/include/asm-i386/paravirt.h
+++ b/include/asm-i386/paravirt.h
@@ -3,8 +3,26 @@
 /* Various instructions on x86 need to be replaced for
  * para-virtualization: those hooks are defined here. */
 #include <linux/linkage.h>
+#include <linux/stringify.h>
 
 #ifdef CONFIG_PARAVIRT
+/* These are the most performance critical ops, so we want to be able to patch
+ * callers */
+#define PARAVIRT_IRQ_DISABLE 0
+#define PARAVIRT_IRQ_ENABLE 1
+#define PARAVIRT_RESTORE_FLAGS 2
+#define PARAVIRT_SAVE_FLAGS 3
+#define PARAVIRT_SAVE_FLAGS_IRQ_DISABLE 4
+#define PARAVIRT_INTERRUPT_RETURN 5
+#define PARAVIRT_STI_SYSEXIT 6
+
+/* Bitmask of what can be clobbered: usually at least eax. */
+#define CLBR_NONE 0x0
+#define CLBR_EAX 0x1
+#define CLBR_ECX 0x2
+#define CLBR_EDX 0x4
+#define CLBR_ANY 0x7
+
 #ifndef __ASSEMBLY__
 struct thread_struct;
 struct Xgt_desc_struct;
@@ -15,6 +33,15 @@ struct paravirt_ops
         int paravirt_enabled;
         const char *name;
 
+        /*
+         * Patch may replace one of the defined code sequences with arbitrary
+         * code, subject to the same register constraints.  This generally
+         * means the code is not free to clobber any registers other than EAX.
+         * The patch function should return the number of bytes of code
+         * generated, as we nop pad the rest in generic code.
+         */
+        unsigned (*patch)(u8 type, u16 clobber, void *firstinsn, unsigned len);
+
         void (*arch_setup)(void);
         char *(*memory_setup)(void);
         void (*init_IRQ)(void);
@@ -147,35 +174,6 @@ static inline void __cpuid(unsigned int *eax, unsigned int *ebx,
 #define read_cr4_safe(x) paravirt_ops.read_cr4_safe()
 #define write_cr4(x) paravirt_ops.write_cr4(x)
 
-static inline unsigned long __raw_local_save_flags(void)
-{
-        return paravirt_ops.save_fl();
-}
-
-static inline void raw_local_irq_restore(unsigned long flags)
-{
-        return paravirt_ops.restore_fl(flags);
-}
-
-static inline void raw_local_irq_disable(void)
-{
-        paravirt_ops.irq_disable();
-}
-
-static inline void raw_local_irq_enable(void)
-{
-        paravirt_ops.irq_enable();
-}
-
-static inline unsigned long __raw_local_irq_save(void)
-{
-        unsigned long flags = paravirt_ops.save_fl();
-
-        paravirt_ops.irq_disable();
-
-        return flags;
-}
-
 static inline void raw_safe_halt(void)
 {
         paravirt_ops.safe_halt();
@@ -267,15 +265,134 @@ static inline void slow_down_io(void) {
 #endif
 }
 
-#define CLI_STRING      "pushl %eax; pushl %ecx; pushl %edx; call *paravirt_ops+PARAVIRT_irq_disable; popl %edx; popl %ecx; popl %eax"
-#define STI_STRING      "pushl %eax; pushl %ecx; pushl %edx; call *paravirt_ops+PARAVIRT_irq_enable; popl %edx; popl %ecx; popl %eax"
+/* These all sit in the .parainstructions section to tell us what to patch. */
+struct paravirt_patch {
+        u8 *instr;              /* original instructions */
+        u8 instrtype;           /* type of this instruction */
+        u8 len;                 /* length of original instruction */
+        u16 clobbers;           /* what registers you may clobber */
+};
+
+#define paravirt_alt(insn_string, typenum, clobber)     \
+        "771:\n\t" insn_string "\n" "772:\n"            \
+        ".pushsection .parainstructions,\"a\"\n"        \
+        "  .long 771b\n"                                \
+        "  .byte " __stringify(typenum) "\n"            \
+        "  .byte 772b-771b\n"                           \
+        "  .short " __stringify(clobber) "\n"           \
+        ".popsection"
+
+static inline unsigned long __raw_local_save_flags(void)
+{
+        unsigned long f;
+
+        __asm__ __volatile__(paravirt_alt( "pushl %%ecx; pushl %%edx;"
+                                           "call *%1;"
+                                           "popl %%edx; popl %%ecx",
+                                          PARAVIRT_SAVE_FLAGS, CLBR_NONE)
+                             : "=a"(f): "m"(paravirt_ops.save_fl)
+                             : "memory", "cc");
+        return f;
+}
+
+static inline void raw_local_irq_restore(unsigned long f)
+{
+        __asm__ __volatile__(paravirt_alt( "pushl %%ecx; pushl %%edx;"
+                                           "call *%1;"
+                                           "popl %%edx; popl %%ecx",
+                                          PARAVIRT_RESTORE_FLAGS, CLBR_EAX)
+                             : "=a"(f) : "m" (paravirt_ops.restore_fl), "0"(f)
+                             : "memory", "cc");
+}
+
+static inline void raw_local_irq_disable(void)
+{
+        __asm__ __volatile__(paravirt_alt( "pushl %%ecx; pushl %%edx;"
+                                           "call *%0;"
+                                           "popl %%edx; popl %%ecx",
+                                          PARAVIRT_IRQ_DISABLE, CLBR_EAX)
+                             : : "m" (paravirt_ops.irq_disable)
+                             : "memory", "eax", "cc");
+}
+
+static inline void raw_local_irq_enable(void)
+{
+        __asm__ __volatile__(paravirt_alt( "pushl %%ecx; pushl %%edx;"
+                                           "call *%0;"
+                                           "popl %%edx; popl %%ecx",
+                                          PARAVIRT_IRQ_ENABLE, CLBR_EAX)
+                             : : "m" (paravirt_ops.irq_enable)
+                             : "memory", "eax", "cc");
+}
+
+static inline unsigned long __raw_local_irq_save(void)
+{
+        unsigned long f;
+
+        __asm__ __volatile__(paravirt_alt( "pushl %%ecx; pushl %%edx;"
+                                           "call *%1; pushl %%eax;"
+                                           "call *%2; popl %%eax;"
+                                           "popl %%edx; popl %%ecx",
+                                          PARAVIRT_SAVE_FLAGS_IRQ_DISABLE,
+                                          CLBR_NONE)
+                             : "=a"(f)
+                             : "m" (paravirt_ops.save_fl),
+                               "m" (paravirt_ops.irq_disable)
+                             : "memory", "cc");
+        return f;
+}
+
+#define CLI_STRING paravirt_alt("pushl %%ecx; pushl %%edx;"             \
+                     "call *paravirt_ops+%c[irq_disable];"              \
+                     "popl %%edx; popl %%ecx",                          \
+                     PARAVIRT_IRQ_DISABLE, CLBR_EAX)
+
+#define STI_STRING paravirt_alt("pushl %%ecx; pushl %%edx;"             \
+                     "call *paravirt_ops+%c[irq_enable];"               \
+                     "popl %%edx; popl %%ecx",                          \
+                     PARAVIRT_IRQ_ENABLE, CLBR_EAX)
+#define CLI_STI_CLOBBERS , "%eax"
+#define CLI_STI_INPUT_ARGS \
+        ,                                                               \
+        [irq_disable] "i" (offsetof(struct paravirt_ops, irq_disable)), \
+        [irq_enable] "i" (offsetof(struct paravirt_ops, irq_enable))
+
 #else  /* __ASSEMBLY__ */
 
-#define INTERRUPT_RETURN        jmp *%cs:paravirt_ops+PARAVIRT_iret
-#define DISABLE_INTERRUPTS      pushl %eax; pushl %ecx; pushl %edx; call *paravirt_ops+PARAVIRT_irq_disable; popl %edx; popl %ecx; popl %eax
-#define ENABLE_INTERRUPTS       pushl %eax; pushl %ecx; pushl %edx; call *%cs:paravirt_ops+PARAVIRT_irq_enable; popl %edx; popl %ecx; popl %eax
-#define ENABLE_INTERRUPTS_SYSEXIT       jmp *%cs:paravirt_ops+PARAVIRT_irq_enable_sysexit
-#define GET_CR0_INTO_EAX        call *paravirt_ops+PARAVIRT_read_cr0
+#define PARA_PATCH(ptype, clobbers, ops)        \
+771:;                                           \
+        ops;                                    \
+772:;                                           \
+        .pushsection .parainstructions,"a";     \
+         .long 771b;                            \
+         .byte ptype;                           \
+         .byte 772b-771b;                       \
+         .short clobbers;                       \
+        .popsection
+
+#define INTERRUPT_RETURN                                \
+        PARA_PATCH(PARAVIRT_INTERRUPT_RETURN, CLBR_ANY, \
+        jmp *%cs:paravirt_ops+PARAVIRT_iret)
+
+#define DISABLE_INTERRUPTS(clobbers)                    \
+        PARA_PATCH(PARAVIRT_IRQ_DISABLE, clobbers,      \
+        pushl %ecx; pushl %edx;                         \
+        call *paravirt_ops+PARAVIRT_irq_disable;        \
+        popl %edx; popl %ecx)                           \
+
+#define ENABLE_INTERRUPTS(clobbers)                     \
+        PARA_PATCH(PARAVIRT_IRQ_ENABLE, clobbers,       \
+        pushl %ecx; pushl %edx;                         \
+        call *%cs:paravirt_ops+PARAVIRT_irq_enable;     \
+        popl %edx; popl %ecx)
+
+#define ENABLE_INTERRUPTS_SYSEXIT                       \
+        PARA_PATCH(PARAVIRT_STI_SYSEXIT, CLBR_ANY,      \
+        jmp *%cs:paravirt_ops+PARAVIRT_irq_enable_sysexit)
+
+#define GET_CR0_INTO_EAX                        \
+        call *paravirt_ops+PARAVIRT_read_cr0
+
 #endif /* __ASSEMBLY__ */
 #endif /* CONFIG_PARAVIRT */
 #endif  /* __ASM_PARAVIRT_H */