[patch 12/32] xen: fix multicall batching

[Jeremy Fitzhardinge]

Disable interrupts between allocating a multicall entry and actually
issuing it, to prevent an interrupt from coming in, allocating and
initializing further multicall entries, and then issuing them all,
including the partially completed one.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xxxxxxxxxxxxx>

---
 arch/i386/xen/enlighten.c  |   44 +++++++++++++++++++++++++++-----------------
 arch/i386/xen/mmu.c        |   18 ++++++++++++------
 arch/i386/xen/multicalls.c |    9 ++++++++-
 arch/i386/xen/multicalls.h |   27 +++++++++++++++++++++++----
 arch/i386/xen/xen-ops.h    |    5 +----
 5 files changed, 71 insertions(+), 32 deletions(-)

===================================================================
--- a/arch/i386/xen/enlighten.c
+++ b/arch/i386/xen/enlighten.c
@@ -187,13 +187,25 @@ static void xen_halt(void)
 
 static void xen_set_lazy_mode(enum paravirt_lazy_mode mode)
 {
-	enum paravirt_lazy_mode *lazy = &get_cpu_var(xen_lazy_mode);
+	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;
+	}
 
 	xen_mc_flush();
-
-	*lazy = mode;
-
-	put_cpu_var(xen_lazy_mode);
+	x86_write_percpu(xen_lazy_mode, mode);
 }
 
 static unsigned long xen_store_tr(void)
@@ -220,7 +232,7 @@ static void xen_set_ldt(const void *addr
 
 	MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);
 
-	xen_mc_issue();
+	xen_mc_issue(PARAVIRT_LAZY_CPU);
 }
 
 static void xen_load_gdt(const struct Xgt_desc_struct *dtr)
@@ -248,7 +260,7 @@ static void xen_load_gdt(const struct Xg
 
 	MULTI_set_gdt(mcs.mc, frames, size / sizeof(struct desc_struct));
 
-	xen_mc_issue();
+	xen_mc_issue(PARAVIRT_LAZY_CPU);
 }
 
 static void load_TLS_descriptor(struct thread_struct *t,
@@ -256,18 +268,20 @@ static void load_TLS_descriptor(struct t
 {
 	struct desc_struct *gdt = get_cpu_gdt_table(cpu);
 	xmaddr_t maddr = virt_to_machine(&gdt[GDT_ENTRY_TLS_MIN+i]);
-	struct multicall_space mc = xen_mc_entry(0);
+	struct multicall_space mc = __xen_mc_entry(0);
 
 	MULTI_update_descriptor(mc.mc, maddr.maddr, t->tls_array[i]);
 }
 
 static void xen_load_tls(struct thread_struct *t, unsigned int cpu)
 {
+	xen_mc_batch();
+
 	load_TLS_descriptor(t, cpu, 0);
 	load_TLS_descriptor(t, cpu, 1);
 	load_TLS_descriptor(t, cpu, 2);
 
-	xen_mc_issue();
+	xen_mc_issue(PARAVIRT_LAZY_CPU);
 }
 
 static void xen_write_ldt_entry(struct desc_struct *dt, int entrynum, u32 low, u32 high)
@@ -387,13 +401,9 @@ static void xen_load_esp0(struct tss_str
 static void xen_load_esp0(struct tss_struct *tss,
 				   struct thread_struct *thread)
 {
-	if (xen_get_lazy_mode() != PARAVIRT_LAZY_CPU) {
-		if (HYPERVISOR_stack_switch(__KERNEL_DS, thread->esp0))
-			BUG();
-	} else {
-		struct multicall_space mcs = xen_mc_entry(0);
-		MULTI_stack_switch(mcs.mc, __KERNEL_DS, thread->esp0);
-	}
+	struct multicall_space mcs = xen_mc_entry(0);
+	MULTI_stack_switch(mcs.mc, __KERNEL_DS, thread->esp0);
+	xen_mc_issue(PARAVIRT_LAZY_CPU);
 }
 
 static void xen_set_iopl_mask(unsigned mask)
@@ -485,7 +495,7 @@ static void xen_write_cr3(unsigned long 
 
 		MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);
 
-		xen_mc_issue();
+		xen_mc_issue(PARAVIRT_LAZY_CPU);
 	}
 }
 
===================================================================
--- a/arch/i386/xen/mmu.c
+++ b/arch/i386/xen/mmu.c
@@ -366,7 +366,7 @@ static int pin_page(struct page *page, u
 	else {
 		void *pt = lowmem_page_address(page);
 		unsigned long pfn = page_to_pfn(page);
-		struct multicall_space mcs = xen_mc_entry(0);
+		struct multicall_space mcs = __xen_mc_entry(0);
 
 		flush = 0;
 
@@ -386,10 +386,12 @@ void xen_pgd_pin(pgd_t *pgd)
 	struct multicall_space mcs;
 	struct mmuext_op *op;
 
+	xen_mc_batch();
+
 	if (pgd_walk(pgd, pin_page, TASK_SIZE))
 		kmap_flush_unused();
 
-	mcs = xen_mc_entry(sizeof(*op));
+	mcs = __xen_mc_entry(sizeof(*op));
 	op = mcs.args;
 
 #ifdef CONFIG_X86_PAE
@@ -400,7 +402,7 @@ void xen_pgd_pin(pgd_t *pgd)
 	op->arg1.mfn = pfn_to_mfn(PFN_DOWN(__pa(pgd)));
 	MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);
 
-	xen_mc_flush();
+	xen_mc_issue(0);
 }
 
 /* The init_mm pagetable is really pinned as soon as its created, but
@@ -424,7 +426,7 @@ static int unpin_page(struct page *page,
 	if (pgfl && !PageHighMem(page)) {
 		void *pt = lowmem_page_address(page);
 		unsigned long pfn = page_to_pfn(page);
-		struct multicall_space mcs = xen_mc_entry(0);
+		struct multicall_space mcs = __xen_mc_entry(0);
 
 		MULTI_update_va_mapping(mcs.mc, (unsigned long)pt,
 					pfn_pte(pfn, PAGE_KERNEL),
@@ -438,7 +440,11 @@ static void xen_pgd_unpin(pgd_t *pgd)
 static void xen_pgd_unpin(pgd_t *pgd)
 {
 	struct mmuext_op *op;
-	struct multicall_space mcs = xen_mc_entry(sizeof(*op));
+	struct multicall_space mcs;
+
+	xen_mc_batch();
+
+	mcs = __xen_mc_entry(sizeof(*op));
 
 	op = mcs.args;
 	op->cmd = MMUEXT_UNPIN_TABLE;
@@ -448,7 +454,7 @@ static void xen_pgd_unpin(pgd_t *pgd)
 
 	pgd_walk(pgd, unpin_page, TASK_SIZE);
 
-	xen_mc_flush();
+	xen_mc_issue(0);
 }
 
 
===================================================================
--- a/arch/i386/xen/multicalls.c
+++ b/arch/i386/xen/multicalls.c
@@ -35,11 +35,17 @@ struct mc_buffer {
 };
 
 static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
+DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);
 
 void xen_mc_flush(void)
 {
 	struct mc_buffer *b = &get_cpu_var(mc_buffer);
 	int ret = 0;
+	unsigned long flags;
+
+	/* Disable interrupts in case someone comes in and queues
+	   something in the middle */
+	local_irq_save(flags);
 
 	if (b->mcidx) {
 		int i;
@@ -55,11 +61,12 @@ void xen_mc_flush(void)
 		BUG_ON(b->argidx != 0);
 
 	put_cpu_var(mc_buffer);
+	local_irq_restore(flags);
 
 	BUG_ON(ret);
 }
 
-struct multicall_space xen_mc_entry(size_t args)
+struct multicall_space __xen_mc_entry(size_t args)
 {
 	struct mc_buffer *b = &get_cpu_var(mc_buffer);
 	struct multicall_space ret;
===================================================================
--- a/arch/i386/xen/multicalls.h
+++ b/arch/i386/xen/multicalls.h
@@ -11,16 +11,35 @@ struct multicall_space
 };
 
 /* Allocate room for a multicall and its args */
-struct multicall_space xen_mc_entry(size_t args);
+struct multicall_space __xen_mc_entry(size_t args);
+
+DECLARE_PER_CPU(unsigned long, xen_mc_irq_flags);
+
+/* Call to start a batch of multiple __xen_mc_entry()s.  Must be
+   paired with xen_mc_issue() */
+static inline void xen_mc_batch(void)
+{
+	/* need to disable interrupts until this entry is complete */
+	local_irq_save(__get_cpu_var(xen_mc_irq_flags));
+}
+
+static inline struct multicall_space xen_mc_entry(size_t args)
+{
+	xen_mc_batch();
+	return __xen_mc_entry(args);
+}
 
 /* Flush all pending multicalls */
 void xen_mc_flush(void);
 
-/* Issue a multicall if we're not in lazy mode */
-static inline void xen_mc_issue(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() == PARAVIRT_LAZY_NONE)
+	if ((xen_get_lazy_mode() & mode) == 0)
 		xen_mc_flush();
+
+	/* restore flags saved in xen_mc_batch */
+	local_irq_restore(x86_read_percpu(xen_mc_irq_flags));
 }
 
 #endif /* _XEN_MULTICALLS_H */
===================================================================
--- a/arch/i386/xen/xen-ops.h
+++ b/arch/i386/xen/xen-ops.h
@@ -26,10 +26,7 @@ DECLARE_PER_CPU(enum paravirt_lazy_mode,
 
 static inline unsigned xen_get_lazy_mode(void)
 {
-	unsigned ret = get_cpu_var(xen_lazy_mode);
-	put_cpu_var(xen_lazy_mode);
-
-	return ret;
+	return x86_read_percpu(xen_lazy_mode);
 }
 
 

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