[patch 29/29] xen: Attempt to patch inline versions of common operations

Jeremy Fitzhardinge
2007-05-04T23:49:26Z

[-- Attachment #1: xen-patch-inline.patch --]
[-- Type: text/plain, Size: 10534 bytes --]

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>
---
arch/i386/kernel/asm-offsets.c | 7 ++
arch/i386/xen/Makefile | 2
arch/i386/xen/enlighten.c | 108 +++++++++++++++++++------------------
arch/i386/xen/xen-asm.S | 114 ++++++++++++++++++++++++++++++++++++++++
arch/i386/xen/xen-ops.h | 13 ++++
5 files changed, 190 insertions(+), 54 deletions(-)

===================================================================
--- a/arch/i386/kernel/asm-offsets.c
+++ b/arch/i386/kernel/asm-offsets.c
@@ -16,6 +16,7 @@
#include <asm/processor.h>
#include <asm/thread_info.h>
#include <asm/elf.h>
+#include <xen/interface/xen.h>

#define DEFINE(sym, val) \
asm volatile("\n->" #sym " %0 " #val : : "i" (val))
@@ -115,4 +116,10 @@ void foo(void)
OFFSET(PARAVIRT_iret, paravirt_ops, iret);
OFFSET(PARAVIRT_read_cr0, paravirt_ops, read_cr0);
#endif
+
+#ifdef CONFIG_XEN
+ BLANK();
+ OFFSET(XEN_vcpu_info_mask, vcpu_info, evtchn_upcall_mask);
+ OFFSET(XEN_vcpu_info_pending, vcpu_info, evtchn_upcall_pending);
+#endif
}
===================================================================
--- a/arch/i386/xen/Makefile
+++ b/arch/i386/xen/Makefile
@@ -1,4 +1,4 @@ obj-y := enlighten.o setup.o features.o
obj-y := enlighten.o setup.o features.o multicalls.o mmu.o \
- events.o time.o
+ events.o time.o xen-asm.o

obj-$(CONFIG_SMP) += smp.o
===================================================================
--- a/arch/i386/xen/enlighten.c
+++ b/arch/i386/xen/enlighten.c
@@ -107,9 +107,11 @@ void xen_vcpu_setup(int cpu)
if (err == 0) {
have_vcpu_info_placement = 1;
per_cpu(xen_vcpu, cpu) = vcpup;
+
printk("cpu %d using vcpu_info at %p\n",
cpu, vcpup);
}
+
}

static void __init xen_banner(void)
@@ -169,20 +171,6 @@ 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;
@@ -209,25 +197,6 @@ static void xen_restore_fl(unsigned long
}
}

-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
@@ -236,12 +205,6 @@ static void xen_irq_disable(void)
preempt_disable();
x86_read_percpu(xen_vcpu)->evtchn_upcall_mask = 1;
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)
@@ -261,19 +224,6 @@ static void xen_irq_enable(void)

barrier(); /* unmask then check (avoid races) */
if (unlikely(vcpu->evtchn_upcall_pending))
- 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();
}

@@ -852,6 +802,57 @@ static __init void xen_pagetable_setup_d
xen_vcpu_setup(smp_processor_id());
}

+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,
@@ -859,7 +860,7 @@ static const struct paravirt_ops xen_par
.name = "Xen",
.banner = xen_banner,

- .patch = paravirt_patch_default,
+ .patch = xen_patch,

.memory_setup = xen_memory_setup,
.arch_setup = xen_arch_setup,
@@ -1035,6 +1036,7 @@ static const struct machine_ops __initda
.crash_shutdown = xen_crash_shutdown,
.emergency_restart = xen_emergency_restart,
};
+

/* First C function to be called on Xen boot */
static asmlinkage void __init xen_start_kernel(void)
===================================================================
--- /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
===================================================================
--- a/arch/i386/xen/xen-ops.h
+++ b/arch/i386/xen/xen-ops.h
@@ -55,4 +55,17 @@ int xen_smp_call_function_mask(cpumask_t
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 */

--