[PATCH RFC 2/2] paravirt: clean up lazy mode handling

[PATCH RFC 2/2] paravirt: clean up lazy mode handling

[Jeremy Fitzhardinge]

[ Changes since last post: fixed up lguest ]

Currently, the set_lazy_mode pv_op is overloaded with 5 functions:
 1. enter lazy cpu mode
 2. leave lazy cpu mode
 3. enter lazy mmu mode
 4. leave lazy mmu mode
 5. flush pending batched operations

This complicates each paravirt backend, since it needs to deal with
all the possible state transitions, handling flushing, etc. In
particular, flushing is quite distinct from the other 4 functions, and
seems to just cause complication.

This patch removes the set_lazy_mode operation, and adds "enter" and
"leave" lazy mode operations on mmu_ops and cpu_ops.  All the logic
associated with enter and leaving lazy states is now in common code
(basically BUG_ONs to make sure that no mode is current when entering
a lazy mode, and make sure that the mode is current when leaving).
Also, flush is handled in a common way, by simply leaving and
re-entering the lazy mode.

The result is that the Xen, lguest and VMI lazy mode implementations
are much simpler.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Andi Kleen <ak@suse.de>
Cc: Zach Amsden <zach@vmware.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Avi Kivity <avi@qumranet.com>
Cc: Anthony Liguory <aliguori@us.ibm.com>
Cc: "Glauber de Oliveira Costa" <glommer@gmail.com>
Cc: "Nakajima, Jun" <jun.nakajima@intel.com>

---
 arch/i386/kernel/paravirt.c |   58 +++++++++++++++++++++++++++++++++++++++----
 arch/i386/kernel/vmi.c      |   45 +++++++++++++++++++--------------
 arch/i386/xen/enlighten.c   |   44 ++++++++++----------------------
 arch/i386/xen/mmu.c         |    2 -
 arch/i386/xen/multicalls.h  |    2 -
 arch/i386/xen/xen-ops.h     |    7 -----
 drivers/lguest/lguest.c     |   34 ++++++++-----------------
 include/asm-i386/paravirt.h |   52 ++++++++++++++++++++++++--------------
 8 files changed, 140 insertions(+), 104 deletions(-)

===================================================================
--- a/arch/i386/kernel/paravirt.c
+++ b/arch/i386/kernel/paravirt.c
@@ -266,6 +266,49 @@ int paravirt_disable_iospace(void)
 	}
 
 	return ret;
+}
+
+static DEFINE_PER_CPU(enum paravirt_lazy_mode, paravirt_lazy_mode) = PARAVIRT_LAZY_NONE;
+
+static inline void enter_lazy(enum paravirt_lazy_mode mode)
+{
+	BUG_ON(x86_read_percpu(paravirt_lazy_mode) != PARAVIRT_LAZY_NONE);
+	BUG_ON(preemptible());
+
+	x86_write_percpu(paravirt_lazy_mode, mode);
+}
+
+void paravirt_leave_lazy(enum paravirt_lazy_mode mode)
+{
+	BUG_ON(x86_read_percpu(paravirt_lazy_mode) != mode);
+	BUG_ON(preemptible());
+
+	x86_write_percpu(paravirt_lazy_mode, PARAVIRT_LAZY_NONE);
+}
+
+void paravirt_enter_lazy_mmu(void)
+{
+	enter_lazy(PARAVIRT_LAZY_MMU);
+}
+
+void paravirt_leave_lazy_mmu(void)
+{
+	paravirt_leave_lazy(PARAVIRT_LAZY_MMU);
+}
+
+void paravirt_enter_lazy_cpu(void)
+{
+	enter_lazy(PARAVIRT_LAZY_CPU);
+}
+
+void paravirt_leave_lazy_cpu(void)
+{
+	paravirt_leave_lazy(PARAVIRT_LAZY_CPU);
+}
+
+enum paravirt_lazy_mode paravirt_get_lazy_mode(void)
+{
+	return x86_read_percpu(paravirt_lazy_mode);
 }
 
 struct pv_info pv_info = {
@@ -334,6 +377,11 @@ struct paravirt_ops paravirt_ops = {
 
 		 .set_iopl_mask = native_set_iopl_mask,
 		 .io_delay = native_io_delay,
+
+		 .lazy_mode = {
+			 .enter = paravirt_nop,
+			 .leave = paravirt_nop,
+		 },
 	 },
 
 	.pv_apic_ops = {
@@ -347,10 +395,6 @@ struct paravirt_ops paravirt_ops = {
 #endif
 	 },
 
-	.pv_misc_ops = {
-		 .set_lazy_mode = paravirt_nop,
-	 },
-
 	.pv_mmu_ops = {
 		 .pagetable_setup_start = native_pagetable_setup_start,
 		 .pagetable_setup_done = native_pagetable_setup_done,
@@ -401,6 +445,11 @@ struct paravirt_ops paravirt_ops = {
 		 .dup_mmap = paravirt_nop,
 		 .exit_mmap = paravirt_nop,
 		 .activate_mm = paravirt_nop,
+
+		 .lazy_mode = {
+			 .enter = paravirt_nop,
+			 .leave = paravirt_nop,
+		 },
 	 },
 };
 
@@ -417,7 +466,6 @@ static void __init __used pv_aliases(voi
 		     : : "i" (offsetof(struct paravirt_ops, inner)))
 
 	substructure(pv_init_ops);
-	substructure(pv_misc_ops);
 	substructure(pv_time_ops);
 	substructure(pv_cpu_ops);
 	substructure(pv_irq_ops);
===================================================================
--- a/arch/i386/kernel/vmi.c
+++ b/arch/i386/kernel/vmi.c
@@ -552,24 +552,22 @@ vmi_startup_ipi_hook(int phys_apicid, un
 }
 #endif
 
-static void vmi_set_lazy_mode(enum paravirt_lazy_mode mode)
-{
-	static DEFINE_PER_CPU(enum paravirt_lazy_mode, lazy_mode);
-
-	if (!vmi_ops.set_lazy_mode)
-		return;
-
-	/* Modes should never nest or overlap */
-	BUG_ON(__get_cpu_var(lazy_mode) && !(mode == PARAVIRT_LAZY_NONE ||
-					     mode == PARAVIRT_LAZY_FLUSH));
-
-	if (mode == PARAVIRT_LAZY_FLUSH) {
-		vmi_ops.set_lazy_mode(0);
-		vmi_ops.set_lazy_mode(__get_cpu_var(lazy_mode));
-	} else {
-		vmi_ops.set_lazy_mode(mode);
-		__get_cpu_var(lazy_mode) = mode;
-	}
+static void vmi_enter_lazy_cpu(void)
+{
+	paravirt_enter_lazy_cpu();
+	vmi_ops.set_lazy_mode(2);
+}
+
+static void vmi_enter_lazy_mmu(void)
+{
+	paravirt_enter_lazy_mmu();
+	vmi_ops.set_lazy_mode(1);
+}
+
+static void vmi_leave_lazy(void)
+{
+	paravirt_leave_lazy(paravirt_get_lazy_mode());
+	vmi_ops.set_lazy_mode(0);
 }
 
 static inline int __init check_vmi_rom(struct vrom_header *rom)
@@ -798,7 +796,16 @@ static inline int __init activate_vmi(vo
 	para_wrap(pv_cpu_ops.load_esp0, vmi_load_esp0, set_kernel_stack, UpdateKernelStack);
 	para_fill(pv_cpu_ops.set_iopl_mask, SetIOPLMask);
 	para_fill(pv_cpu_ops.io_delay, IODelay);
-	para_wrap(pv_misc_ops.set_lazy_mode, vmi_set_lazy_mode, set_lazy_mode, SetLazyMode);
+
+	para_wrap(pv_cpu_ops.lazy_mode.enter, vmi_enter_lazy_cpu,
+		  set_lazy_mode, SetLazyMode);
+	para_wrap(pv_cpu_ops.lazy_mode.leave, vmi_leave_lazy,
+		  set_lazy_mode, SetLazyMode);
+
+	para_wrap(pv_mmu_ops.lazy_mode.enter, vmi_enter_lazy_mmu,
+		  set_lazy_mode, SetLazyMode);
+	para_wrap(pv_mmu_ops.lazy_mode.leave, vmi_leave_lazy,
+		  set_lazy_mode, SetLazyMode);
 
 	/* user and kernel flush are just handled with different flags to FlushTLB */
 	para_wrap(pv_mmu_ops.flush_tlb_user, vmi_flush_tlb_user, _flush_tlb, FlushTLB);
===================================================================
--- a/arch/i386/xen/enlighten.c
+++ b/arch/i386/xen/enlighten.c
@@ -50,8 +50,6 @@
 #include "multicalls.h"
 
 EXPORT_SYMBOL_GPL(hypercall_page);
-
-DEFINE_PER_CPU(enum paravirt_lazy_mode, xen_lazy_mode);
 
 DEFINE_PER_CPU(struct vcpu_info *, xen_vcpu);
 DEFINE_PER_CPU(struct vcpu_info, xen_vcpu_info);
@@ -264,29 +262,10 @@ static void xen_halt(void)
 		xen_safe_halt();
 }
 
-static void xen_set_lazy_mode(enum paravirt_lazy_mode mode)
-{
-	BUG_ON(preemptible());
-
-	switch (mode) {
-	case PARAVIRT_LAZY_NONE:
-		BUG_ON(x86_read_percpu(xen_lazy_mode) == PARAVIRT_LAZY_NONE);
-		break;
-
-	case PARAVIRT_LAZY_MMU:
-	case PARAVIRT_LAZY_CPU:
-		BUG_ON(x86_read_percpu(xen_lazy_mode) != PARAVIRT_LAZY_NONE);
-		break;
-
-	case PARAVIRT_LAZY_FLUSH:
-		/* flush if necessary, but don't change state */
-		if (x86_read_percpu(xen_lazy_mode) != PARAVIRT_LAZY_NONE)
-			xen_mc_flush();
-		return;
-	}
-
+static void xen_leave_lazy(void)
+{
+	paravirt_leave_lazy(paravirt_get_lazy_mode());
 	xen_mc_flush();
-	x86_write_percpu(xen_lazy_mode, mode);
 }
 
 static unsigned long xen_store_tr(void)
@@ -373,7 +352,7 @@ static void xen_load_tls(struct thread_s
 	 * loaded properly.  This will go away as soon as Xen has been
 	 * modified to not save/restore %gs for normal hypercalls.
 	 */
-	if (xen_get_lazy_mode() == PARAVIRT_LAZY_CPU)
+	if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_CPU)
 		loadsegment(gs, 0);
 }
 
@@ -993,6 +972,11 @@ static const struct pv_cpu_ops xen_cpu_o
 
 	.set_iopl_mask = xen_set_iopl_mask,
 	.io_delay = xen_io_delay,
+
+	.lazy_mode = {
+		.enter = paravirt_enter_lazy_cpu,
+		.leave = xen_leave_lazy,
+	},
 };
 
 static const struct pv_irq_ops xen_irq_ops __initdata = {
@@ -1068,10 +1052,11 @@ static const struct pv_mmu_ops xen_mmu_o
 	.activate_mm = xen_activate_mm,
 	.dup_mmap = xen_dup_mmap,
 	.exit_mmap = xen_exit_mmap,
-};
-
-static const struct pv_misc_ops xen_misc_ops __initdata = {
-	.set_lazy_mode = xen_set_lazy_mode,
+
+	.lazy_mode = {
+		.enter = paravirt_enter_lazy_mmu,
+		.leave = xen_leave_lazy,
+	},
 };
 
 #ifdef CONFIG_SMP
@@ -1156,7 +1141,6 @@ asmlinkage void __init xen_start_kernel(
 	pv_irq_ops = xen_irq_ops;
 	pv_apic_ops = xen_apic_ops;
 	pv_mmu_ops = xen_mmu_ops;
-	pv_misc_ops = xen_misc_ops;
 
 	machine_ops = xen_machine_ops;
 
===================================================================
--- a/arch/i386/xen/mmu.c
+++ b/arch/i386/xen/mmu.c
@@ -154,7 +154,7 @@ void xen_set_pte_at(struct mm_struct *mm
 		    pte_t *ptep, pte_t pteval)
 {
 	if (mm == current->mm || mm == &init_mm) {
-		if (xen_get_lazy_mode() == PARAVIRT_LAZY_MMU) {
+		if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_MMU) {
 			struct multicall_space mcs;
 			mcs = xen_mc_entry(0);
 
===================================================================
--- a/arch/i386/xen/multicalls.h
+++ b/arch/i386/xen/multicalls.h
@@ -35,7 +35,7 @@ void xen_mc_flush(void);
 /* Issue a multicall if we're not in a lazy mode */
 static inline void xen_mc_issue(unsigned mode)
 {
-	if ((xen_get_lazy_mode() & mode) == 0)
+	if ((paravirt_get_lazy_mode() & mode) == 0)
 		xen_mc_flush();
 
 	/* restore flags saved in xen_mc_batch */
===================================================================
--- a/arch/i386/xen/xen-ops.h
+++ b/arch/i386/xen/xen-ops.h
@@ -32,13 +32,6 @@ bool xen_vcpu_stolen(int vcpu);
 
 void xen_mark_init_mm_pinned(void);
 
-DECLARE_PER_CPU(enum paravirt_lazy_mode, xen_lazy_mode);
-
-static inline unsigned xen_get_lazy_mode(void)
-{
-	return x86_read_percpu(xen_lazy_mode);
-}
-
 void __init xen_fill_possible_map(void);
 
 void __init xen_setup_vcpu_info_placement(void);
===================================================================
--- a/drivers/lguest/lguest.c
+++ b/drivers/lguest/lguest.c
@@ -97,29 +97,17 @@ static cycle_t clock_base;
  * them as a batch when lazy_mode is eventually turned off.  Because hypercalls
  * are reasonably expensive, batching them up makes sense.  For example, a
  * large mmap might update dozens of page table entries: that code calls
- * lguest_lazy_mode(PARAVIRT_LAZY_MMU), does the dozen updates, then calls
- * lguest_lazy_mode(PARAVIRT_LAZY_NONE).
+ * paravirt_enter_lazy_mmu(), does the dozen updates, then calls
+ * lguest_leave_lazy_mode().
  *
  * So, when we're in lazy mode, we call async_hypercall() to store the call for
  * future processing.  When lazy mode is turned off we issue a hypercall to
  * flush the stored calls.
- *
- * There's also a hack where "mode" is set to "PARAVIRT_LAZY_FLUSH" which
- * indicates we're to flush any outstanding calls immediately.  This is used
- * when an interrupt handler does a kmap_atomic(): the page table changes must
- * happen immediately even if we're in the middle of a batch.  Usually we're
- * not, though, so there's nothing to do. */
-static enum paravirt_lazy_mode lazy_mode; /* Note: not SMP-safe! */
-static void lguest_lazy_mode(enum paravirt_lazy_mode mode)
-{
-	if (mode == PARAVIRT_LAZY_FLUSH) {
-		if (unlikely(lazy_mode != PARAVIRT_LAZY_NONE))
-			hcall(LHCALL_FLUSH_ASYNC, 0, 0, 0);
-	} else {
-		lazy_mode = mode;
-		if (mode == PARAVIRT_LAZY_NONE)
-			hcall(LHCALL_FLUSH_ASYNC, 0, 0, 0);
-	}
+ */
+static void lguest_leave_lazy_mode(void)
+{
+	hcall(LHCALL_FLUSH_ASYNC, 0, 0, 0);
+	paravirt_leave_lazy(paravirt_get_lazy_mode());
 }
 
 static void lazy_hcall(unsigned long call,
@@ -127,7 +115,7 @@ static void lazy_hcall(unsigned long cal
 		       unsigned long arg2,
 		       unsigned long arg3)
 {
-	if (lazy_mode == PARAVIRT_LAZY_NONE)
+	if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE)
 		hcall(call, arg1, arg2, arg3);
 	else
 		async_hcall(call, arg1, arg2, arg3);
@@ -1011,6 +999,8 @@ __init void lguest_init(void *boot)
 	pv_cpu_ops.write_gdt_entry = lguest_write_gdt_entry;
 	pv_cpu_ops.write_idt_entry = lguest_write_idt_entry;
 	pv_cpu_ops.wbinvd = lguest_wbinvd;
+	pv_cpu_ops.lazy_mode.enter = paravirt_enter_lazy_cpu;
+	pv_cpu_ops.lazy_mode.leave = lguest_leave_lazy_mode;
 
 	/* pagetable management */
 	pv_mmu_ops.write_cr3 = lguest_write_cr3;
@@ -1022,6 +1012,8 @@ __init void lguest_init(void *boot)
 	pv_mmu_ops.set_pmd = lguest_set_pmd;
 	pv_mmu_ops.read_cr2 = lguest_read_cr2;
 	pv_mmu_ops.read_cr3 = lguest_read_cr3;
+	pv_mmu_ops.lazy_mode.enter = paravirt_enter_lazy_mmu;
+	pv_mmu_ops.lazy_mode.leave = lguest_leave_lazy_mode;
 
 #ifdef CONFIG_X86_LOCAL_APIC
 	/* apic read/write intercepts */
@@ -1033,8 +1025,6 @@ __init void lguest_init(void *boot)
 	/* time operations */
 	pv_time_ops.get_wallclock = lguest_get_wallclock;
 	pv_time_ops.time_init = lguest_time_init;
-
-	pv_misc_ops.set_lazy_mode = lguest_lazy_mode;
 
 	/* Now is a good time to look at the implementations of these functions
 	 * before returning to the rest of lguest_init(). */
===================================================================
--- a/include/asm-i386/paravirt.h
+++ b/include/asm-i386/paravirt.h
@@ -24,15 +24,6 @@ struct tss_struct;
 struct tss_struct;
 struct mm_struct;
 struct desc_struct;
-
-/* Lazy mode for batching updates / context switch */
-enum paravirt_lazy_mode {
-	PARAVIRT_LAZY_NONE = 0,
-	PARAVIRT_LAZY_MMU = 1,
-	PARAVIRT_LAZY_CPU = 2,
-	PARAVIRT_LAZY_FLUSH = 3,
-};
-
 
 /* general info */
 struct pv_info {
@@ -64,9 +55,10 @@ struct pv_init_ops {
 };
 
 
-struct pv_misc_ops {
+struct pv_lazy_ops {
 	/* Set deferred update mode, used for batching operations. */
-	void (*set_lazy_mode)(enum paravirt_lazy_mode mode);
+	void (*enter)(void);
+	void (*leave)(void);
 };
 
 struct pv_time_ops {
@@ -131,6 +123,8 @@ struct pv_cpu_ops {
 	/* These two are jmp to, not actually called. */
 	void (*irq_enable_sysexit)(void);
 	void (*iret)(void);
+
+	struct pv_lazy_ops lazy_mode;
 };
 
 struct pv_irq_ops {
@@ -244,12 +238,13 @@ struct pv_mmu_ops {
 #ifdef CONFIG_HIGHPTE
 	void *(*kmap_atomic_pte)(struct page *page, enum km_type type);
 #endif
+
+	struct pv_lazy_ops lazy_mode;
 };
 
 struct paravirt_ops
 {
 	struct pv_init_ops pv_init_ops;
-	struct pv_misc_ops pv_misc_ops;
 	struct pv_time_ops pv_time_ops;
 	struct pv_cpu_ops pv_cpu_ops;
 	struct pv_irq_ops pv_irq_ops;
@@ -259,7 +254,6 @@ struct paravirt_ops
 
 extern struct pv_info pv_info;
 extern struct pv_init_ops pv_init_ops;
-extern struct pv_misc_ops pv_misc_ops;
 extern struct pv_time_ops pv_time_ops;
 extern struct pv_cpu_ops pv_cpu_ops;
 extern struct pv_irq_ops pv_irq_ops;
@@ -950,37 +944,57 @@ static inline void set_pmd(pmd_t *pmdp, 
 }
 #endif	/* CONFIG_X86_PAE */
 
+/* Lazy mode for batching updates / context switch */
+enum paravirt_lazy_mode {
+	PARAVIRT_LAZY_NONE,
+	PARAVIRT_LAZY_MMU,
+	PARAVIRT_LAZY_CPU,
+};
+
+enum paravirt_lazy_mode paravirt_get_lazy_mode(void);
+void paravirt_enter_lazy_cpu(void);
+void paravirt_leave_lazy_cpu(void);
+void paravirt_enter_lazy_mmu(void);
+void paravirt_leave_lazy_mmu(void);
+void paravirt_leave_lazy(enum paravirt_lazy_mode mode);
+
 #define  __HAVE_ARCH_ENTER_LAZY_CPU_MODE
 static inline void arch_enter_lazy_cpu_mode(void)
 {
-	PVOP_VCALL1(pv_misc_ops.set_lazy_mode, PARAVIRT_LAZY_CPU);
+	PVOP_VCALL0(pv_cpu_ops.lazy_mode.enter);
 }
 
 static inline void arch_leave_lazy_cpu_mode(void)
 {
-	PVOP_VCALL1(pv_misc_ops.set_lazy_mode, PARAVIRT_LAZY_NONE);
+	PVOP_VCALL0(pv_cpu_ops.lazy_mode.leave);
 }
 
 static inline void arch_flush_lazy_cpu_mode(void)
 {
-	PVOP_VCALL1(pv_misc_ops.set_lazy_mode, PARAVIRT_LAZY_FLUSH);
+	if (unlikely(paravirt_get_lazy_mode() == PARAVIRT_LAZY_CPU)) {
+		arch_leave_lazy_cpu_mode();
+		arch_enter_lazy_cpu_mode();
+	}
 }
 
 
 #define  __HAVE_ARCH_ENTER_LAZY_MMU_MODE
 static inline void arch_enter_lazy_mmu_mode(void)
 {
-	PVOP_VCALL1(pv_misc_ops.set_lazy_mode, PARAVIRT_LAZY_MMU);
+	PVOP_VCALL0(pv_mmu_ops.lazy_mode.enter);
 }
 
 static inline void arch_leave_lazy_mmu_mode(void)
 {
-	PVOP_VCALL1(pv_misc_ops.set_lazy_mode, PARAVIRT_LAZY_NONE);
+	PVOP_VCALL0(pv_mmu_ops.lazy_mode.leave);
 }
 
 static inline void arch_flush_lazy_mmu_mode(void)
 {
-	PVOP_VCALL1(pv_misc_ops.set_lazy_mode, PARAVIRT_LAZY_FLUSH);
+	if (unlikely(paravirt_get_lazy_mode() == PARAVIRT_LAZY_MMU)) {
+		arch_leave_lazy_mmu_mode();
+		arch_enter_lazy_mmu_mode();
+	}
 }
 
 void _paravirt_nop(void);

Re: [PATCH RFC 2/2] paravirt: clean up lazy mode handling

[Rusty Russell]

On Saturday 13 October 2007 06:40:36 Jeremy Fitzhardinge wrote:
> [ Changes since last post: fixed up lguest ]

This is really nice.  Thanks Jeremy!

This will conflict a little with my own churn (file movement), but no great 
drama if it goes in soon.

Acked-by: Rusty Russell <rusty@rustcorp.com.au>

Re: [PATCH RFC 2/2] paravirt: clean up lazy mode handling

[Glauber de Oliveira Costa]

On 10/12/07, Jeremy Fitzhardinge <jeremy@goop.org> wrote:
> [ Changes since last post: fixed up lguest ]
>
> Currently, the set_lazy_mode pv_op is overloaded with 5 functions:
>  1. enter lazy cpu mode
>  2. leave lazy cpu mode
>  3. enter lazy mmu mode
>  4. leave lazy mmu mode
>  5. flush pending batched operations
>
> This complicates each paravirt backend, since it needs to deal with
> all the possible state transitions, handling flushing, etc. In
> particular, flushing is quite distinct from the other 4 functions, and
> seems to just cause complication.
>
> This patch removes the set_lazy_mode operation, and adds "enter" and
> "leave" lazy mode operations on mmu_ops and cpu_ops.  All the logic
> associated with enter and leaving lazy states is now in common code
> (basically BUG_ONs to make sure that no mode is current when entering
> a lazy mode, and make sure that the mode is current when leaving).
> Also, flush is handled in a common way, by simply leaving and
> re-entering the lazy mode.
>
> The result is that the Xen, lguest and VMI lazy mode implementations
> are much simpler.
>
> Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
> Cc: Andi Kleen <ak@suse.de>
> Cc: Zach Amsden <zach@vmware.com>
> Cc: Rusty Russell <rusty@rustcorp.com.au>
> Cc: Avi Kivity <avi@qumranet.com>
> Cc: Anthony Liguory <aliguori@us.ibm.com>
> Cc: "Glauber de Oliveira Costa" <glommer@gmail.com>
> Cc: "Nakajima, Jun" <jun.nakajima@intel.com>
>
> ---
>  arch/i386/kernel/paravirt.c |   58 +++++++++++++++++++++++++++++++++++++++----
>  arch/i386/kernel/vmi.c      |   45 +++++++++++++++++++--------------
>  arch/i386/xen/enlighten.c   |   44 ++++++++++----------------------
>  arch/i386/xen/mmu.c         |    2 -
>  arch/i386/xen/multicalls.h  |    2 -
>  arch/i386/xen/xen-ops.h     |    7 -----
>  drivers/lguest/lguest.c     |   34 ++++++++-----------------
>  include/asm-i386/paravirt.h |   52 ++++++++++++++++++++++++--------------
>  8 files changed, 140 insertions(+), 104 deletions(-)
>
> ===================================================================
> --- a/arch/i386/kernel/paravirt.c
> +++ b/arch/i386/kernel/paravirt.c
> @@ -266,6 +266,49 @@ int paravirt_disable_iospace(void)
>         }
>
>         return ret;
> +}
> +
> +static DEFINE_PER_CPU(enum paravirt_lazy_mode, paravirt_lazy_mode) = PARAVIRT_LAZY_NONE;
> +
> +static inline void enter_lazy(enum paravirt_lazy_mode mode)
> +{
> +       BUG_ON(x86_read_percpu(paravirt_lazy_mode) != PARAVIRT_LAZY_NONE);
> +       BUG_ON(preemptible());
Wouldn't it be better to WARN_ON, and simply not entering lazy mode?
It does not sound like a fatal condition.

> +void paravirt_leave_lazy(enum paravirt_lazy_mode mode)
> +{
> +       BUG_ON(x86_read_percpu(paravirt_lazy_mode) != mode);
> +       BUG_ON(preemptible());

Although this one seems like a fatal condition ;-)

> +void paravirt_enter_lazy_mmu(void)
> +{
> +       enter_lazy(PARAVIRT_LAZY_MMU);
> +}
> +
> +void paravirt_leave_lazy_mmu(void)
> +{
> +       paravirt_leave_lazy(PARAVIRT_LAZY_MMU);
> +}
> +
> +void paravirt_enter_lazy_cpu(void)
> +{
> +       enter_lazy(PARAVIRT_LAZY_CPU);
> +}
> +
> +void paravirt_leave_lazy_cpu(void)
> +{
> +       paravirt_leave_lazy(PARAVIRT_LAZY_CPU);
> +}
> +
> +enum paravirt_lazy_mode paravirt_get_lazy_mode(void)
> +{
> +       return x86_read_percpu(paravirt_lazy_mode);
>  }

I am concerned that this is 32-bit specific.
But hey: We could wrap it here, but the best solution may be just to
define this macro for 64-bit, and make it everyone benefits. So yeah,
this is a concern here, but I don't think anything should be changed
in this patch to address it so... so... ok ;-)

-- 
Glauber de Oliveira Costa.
"Free as in Freedom"
http://glommer.net

"The less confident you are, the more serious you have to act."