xen: Attempt to patch inline versions of common operations

This patchs adds the mechanism to allow us to patch inline versions of
common operations.

The implementations of the direct-access versions save_fl, restore_fl,
irq_enable and irq_disable are now in assembler, and the same code is
used for both out of line and inline uses.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Keir Fraser <keir@xensource.com>

4 files changed, 182 insertions, 54 deletions

diff --git a/arch/i386/xen/Makefile b/arch/i386/xen/Makefile
index 7bf2ce399a2a..343df246bd3e 100644
--- a/arch/i386/xen/Makefile
+++ b/arch/i386/xen/Makefile
@@ -1,4 +1,4 @@
 obj-y           := enlighten.o setup.o features.o multicalls.o mmu.o \
-                        events.o time.o manage.o
+                        events.o time.o manage.o xen-asm.o
 
 obj-$(CONFIG_SMP)       += smp.o
diff --git a/arch/i386/xen/enlighten.c b/arch/i386/xen/enlighten.c
index e33fa0990eda..4fa62a4cb7cc 100644
--- a/arch/i386/xen/enlighten.c
+++ b/arch/i386/xen/enlighten.c
@@ -115,6 +115,7 @@ static void __init xen_vcpu_setup(int cpu)
                 /* This cpu is using the registered vcpu info, even if
                    later ones fail to. */
                 per_cpu(xen_vcpu, cpu) = vcpup;
+
                 printk(KERN_DEBUG "cpu %d using vcpu_info at %p\n",
                        cpu, vcpup);
         }
@@ -177,20 +178,6 @@ static unsigned long xen_save_fl(void)
         return (-flags) & X86_EFLAGS_IF;
 }
 
-static unsigned long xen_save_fl_direct(void)
-{
-        unsigned long flags;
-
-        /* flag has opposite sense of mask */
-        flags = !x86_read_percpu(xen_vcpu_info.evtchn_upcall_mask);
-
-        /* convert to IF type flag
-           -0 -> 0x00000000
-           -1 -> 0xffffffff
-        */
-        return (-flags) & X86_EFLAGS_IF;
-}
-
 static void xen_restore_fl(unsigned long flags)
 {
         struct vcpu_info *vcpu;
@@ -217,25 +204,6 @@ static void xen_restore_fl(unsigned long flags)
         }
 }
 
-static void xen_restore_fl_direct(unsigned long flags)
-{
-        /* convert from IF type flag */
-        flags = !(flags & X86_EFLAGS_IF);
-
-        /* This is an atomic update, so no need to worry about
-           preemption. */
-        x86_write_percpu(xen_vcpu_info.evtchn_upcall_mask, flags);
-
-        /* If we get preempted here, then any pending event will be
-           handled anyway. */
-
-        if (flags == 0) {
-                barrier(); /* unmask then check (avoid races) */
-                if (unlikely(x86_read_percpu(xen_vcpu_info.evtchn_upcall_pending)))
-                        force_evtchn_callback();
-        }
-}
-
 static void xen_irq_disable(void)
 {
         /* There's a one instruction preempt window here.  We need to
@@ -246,12 +214,6 @@ static void xen_irq_disable(void)
         preempt_enable_no_resched();
 }
 
-static void xen_irq_disable_direct(void)
-{
-        /* Atomic update, so preemption not a concern. */
-        x86_write_percpu(xen_vcpu_info.evtchn_upcall_mask, 1);
-}
-
 static void xen_irq_enable(void)
 {
         struct vcpu_info *vcpu;
@@ -272,19 +234,6 @@ static void xen_irq_enable(void)
                 force_evtchn_callback();
 }
 
-static void xen_irq_enable_direct(void)
-{
-        /* Atomic update, so preemption not a concern. */
-        x86_write_percpu(xen_vcpu_info.evtchn_upcall_mask, 0);
-
-        /* Doesn't matter if we get preempted here, because any
-           pending event will get dealt with anyway. */
-
-        barrier(); /* unmask then check (avoid races) */
-        if (unlikely(x86_read_percpu(xen_vcpu_info.evtchn_upcall_pending)))
-                force_evtchn_callback();
-}
-
 static void xen_safe_halt(void)
 {
         /* Blocking includes an implicit local_irq_enable(). */
@@ -892,6 +841,57 @@ void __init xen_setup_vcpu_info_placement(void)
         }
 }
 
+static unsigned xen_patch(u8 type, u16 clobbers, void *insns, unsigned len)
+{
+        char *start, *end, *reloc;
+        unsigned ret;
+
+        start = end = reloc = NULL;
+
+#define SITE(x)                                                         \
+        case PARAVIRT_PATCH(x):                                         \
+        if (have_vcpu_info_placement) {                                 \
+                start = (char *)xen_##x##_direct;                       \
+                end = xen_##x##_direct_end;                             \
+                reloc = xen_##x##_direct_reloc;                         \
+        }                                                               \
+        goto patch_site
+
+        switch (type) {
+                SITE(irq_enable);
+                SITE(irq_disable);
+                SITE(save_fl);
+                SITE(restore_fl);
+#undef SITE
+
+        patch_site:
+                if (start == NULL || (end-start) > len)
+                        goto default_patch;
+
+                ret = paravirt_patch_insns(insns, len, start, end);
+
+                /* Note: because reloc is assigned from something that
+                   appears to be an array, gcc assumes it's non-null,
+                   but doesn't know its relationship with start and
+                   end. */
+                if (reloc > start && reloc < end) {
+                        int reloc_off = reloc - start;
+                        long *relocp = (long *)(insns + reloc_off);
+                        long delta = start - (char *)insns;
+
+                        *relocp += delta;
+                }
+                break;
+
+        default_patch:
+        default:
+                ret = paravirt_patch_default(type, clobbers, insns, len);
+                break;
+        }
+
+        return ret;
+}
+
 static const struct paravirt_ops xen_paravirt_ops __initdata = {
         .paravirt_enabled = 1,
         .shared_kernel_pmd = 0,
@@ -899,7 +899,7 @@ static const struct paravirt_ops xen_paravirt_ops __initdata = {
         .name = "Xen",
         .banner = xen_banner,
 
-        .patch = paravirt_patch_default,
+        .patch = xen_patch,
 
         .memory_setup = xen_memory_setup,
         .arch_setup = xen_arch_setup,
@@ -1076,6 +1076,7 @@ static const struct machine_ops __initdata xen_machine_ops = {
         .emergency_restart = xen_emergency_restart,
 };
 
+
 /* First C function to be called on Xen boot */
 asmlinkage void __init xen_start_kernel(void)
 {
diff --git a/arch/i386/xen/xen-asm.S b/arch/i386/xen/xen-asm.S
new file mode 100644
index 000000000000..dc4d36d51bc1
--- /dev/null
+++ b/arch/i386/xen/xen-asm.S
@@ -0,0 +1,114 @@
+/*
+        Asm versions of Xen pv-ops, suitable for either direct use or inlining.
+        The inline versions are the same as the direct-use versions, with the
+        pre- and post-amble chopped off.
+
+        This code is encoded for size rather than absolute efficiency,
+        with a view to being able to inline as much as possible.
+
+        We only bother with direct forms (ie, vcpu in pda) of the operations
+        here; the indirect forms are better handled in C, since they're
+        generally too large to inline anyway.
+ */
+
+#include <linux/linkage.h>
+#include <asm/asm-offsets.h>
+#include <asm/thread_info.h>
+#include <asm/percpu.h>
+#include <asm/asm-offsets.h>
+#include <asm/processor-flags.h>
+
+#define RELOC(x, v)     .globl x##_reloc; x##_reloc=v
+#define ENDPATCH(x)     .globl x##_end; x##_end=.
+
+/*
+        Enable events.  This clears the event mask and tests the pending
+        event status with one and operation.  If there are pending
+        events, then enter the hypervisor to get them handled.
+ */
+ENTRY(xen_irq_enable_direct)
+        /* Clear mask and test pending */
+        andw $0x00ff, PER_CPU_VAR(xen_vcpu_info)+XEN_vcpu_info_pending
+        /* Preempt here doesn't matter because that will deal with
+           any pending interrupts.  The pending check may end up being
+           run on the wrong CPU, but that doesn't hurt. */
+        jz 1f
+2:      call check_events
+1:
+ENDPATCH(xen_irq_enable_direct)
+        ret
+        ENDPROC(xen_irq_enable_direct)
+        RELOC(xen_irq_enable_direct, 2b+1)
+
+
+/*
+        Disabling events is simply a matter of making the event mask
+        non-zero.
+ */
+ENTRY(xen_irq_disable_direct)
+        movb $1, PER_CPU_VAR(xen_vcpu_info)+XEN_vcpu_info_mask
+ENDPATCH(xen_irq_disable_direct)
+        ret
+        ENDPROC(xen_irq_disable_direct)
+        RELOC(xen_irq_disable_direct, 0)
+
+/*
+        (xen_)save_fl is used to get the current interrupt enable status.
+        Callers expect the status to be in X86_EFLAGS_IF, and other bits
+        may be set in the return value.  We take advantage of this by
+        making sure that X86_EFLAGS_IF has the right value (and other bits
+        in that byte are 0), but other bits in the return value are
+        undefined.  We need to toggle the state of the bit, because
+        Xen and x86 use opposite senses (mask vs enable).
+ */
+ENTRY(xen_save_fl_direct)
+        testb $0xff, PER_CPU_VAR(xen_vcpu_info)+XEN_vcpu_info_mask
+        setz %ah
+        addb %ah,%ah
+ENDPATCH(xen_save_fl_direct)
+        ret
+        ENDPROC(xen_save_fl_direct)
+        RELOC(xen_save_fl_direct, 0)
+
+
+/*
+        In principle the caller should be passing us a value return
+        from xen_save_fl_direct, but for robustness sake we test only
+        the X86_EFLAGS_IF flag rather than the whole byte. After
+        setting the interrupt mask state, it checks for unmasked
+        pending events and enters the hypervisor to get them delivered
+        if so.
+ */
+ENTRY(xen_restore_fl_direct)
+        testb $X86_EFLAGS_IF>>8, %ah
+        setz %al
+        movb %al, PER_CPU_VAR(xen_vcpu_info)+XEN_vcpu_info_mask
+        /* Preempt here doesn't matter because that will deal with
+           any pending interrupts.  The pending check may end up being
+           run on the wrong CPU, but that doesn't hurt. */
+
+        /* check for pending but unmasked */
+        cmpw $0x0001, PER_CPU_VAR(xen_vcpu_info)+XEN_vcpu_info_pending
+        jz 1f
+2:      call check_events
+1:
+ENDPATCH(xen_restore_fl_direct)
+        ret
+        ENDPROC(xen_restore_fl_direct)
+        RELOC(xen_restore_fl_direct, 2b+1)
+
+
+
+/*
+        Force an event check by making a hypercall,
+        but preserve regs before making the call.
+ */
+check_events:
+        push %eax
+        push %ecx
+        push %edx
+        call force_evtchn_callback
+        pop %edx
+        pop %ecx
+        pop %eax
+        ret
diff --git a/arch/i386/xen/xen-ops.h b/arch/i386/xen/xen-ops.h
index 5b56f7fecd19..33e4c8a16289 100644
--- a/arch/i386/xen/xen-ops.h
+++ b/arch/i386/xen/xen-ops.h
@@ -54,4 +54,17 @@ int xen_smp_call_function_single(int cpu, void (*func) (void *info), void *info,
 int xen_smp_call_function_mask(cpumask_t mask, void (*func)(void *),
                                void *info, int wait);
 
+
+/* Declare an asm function, along with symbols needed to make it
+   inlineable */
+#define DECL_ASM(ret, name, ...)                \
+        ret name(__VA_ARGS__);                  \
+        extern char name##_end[];               \
+        extern char name##_reloc[]              \
+
+DECL_ASM(void, xen_irq_enable_direct, void);
+DECL_ASM(void, xen_irq_disable_direct, void);
+DECL_ASM(unsigned long, xen_save_fl_direct, void);
+DECL_ASM(void, xen_restore_fl_direct, unsigned long);
+
 #endif /* XEN_OPS_H */