Date:	Thu, 25 Feb 2010 23:56:02 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	rt-users <linux-rt-users@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Clark Williams <williams@...hat.com>, nando@...ma.Stanford.EDU,
	Carsten Emde <ce@...g.ch>
Subject: Re: [ANNOUNCE] 2.6.33-rc8-rt2

On Wed, 2010-02-24 at 23:38 +0100, Peter Zijlstra wrote:
> On Wed, 2010-02-24 at 17:52 +0100, Thomas Gleixner wrote:
> > 
> >     - the highmem problem which Fernando reported with i915 on 32bit
> >       i386 is not yet solved. 
> 
> The below compiles and boots a i386 defconfig kernel in kvm, I don't
> have a system with 32bit userspace and i915 handy further test this.
> 

The below seems to boot on 32bit with i915, but since the box was
headless not much was thrown at it.


---
 arch/x86/include/asm/highmem.h |    9 ++-
 arch/x86/mm/highmem_32.c       |   27 +++++---
 arch/x86/mm/iomap_32.c         |   32 +--------
 mm/highmem.c                   |  152 +++++++++++++++++++++++++++------------
 4 files changed, 130 insertions(+), 90 deletions(-)

diff --git a/arch/x86/include/asm/highmem.h b/arch/x86/include/asm/highmem.h
index 433ae1f..8279657 100644
--- a/arch/x86/include/asm/highmem.h
+++ b/arch/x86/include/asm/highmem.h
@@ -55,14 +55,17 @@ extern unsigned long highstart_pfn, highend_pfn;
 #define PKMAP_ADDR(nr)  (PKMAP_BASE + ((nr) << PAGE_SHIFT))
 
 extern void *kmap_high(struct page *page);
+extern void *kmap_pfn_prot(unsigned long pfn, pgprot_t prot);
 extern void kunmap_high(struct page *page);
 
 void *kmap(struct page *page);
+void *kmap_page_prot(struct page *page, pgprot_t prot);
 extern void kunmap_virt(void *ptr);
 extern struct page *kmap_to_page(void *ptr);
 void kunmap(struct page *page);
 
 void *__kmap_atomic_prot(struct page *page, enum km_type type, pgprot_t prot);
+void *__kmap_atomic_prot_pfn(unsigned long pfn, enum km_type type, pgprot_t prot);
 void *__kmap_atomic(struct page *page, enum km_type type);
 void *__kmap_atomic_direct(struct page *page, enum km_type type);
 void __kunmap_atomic(void *kvaddr, enum km_type type);
@@ -85,15 +88,17 @@ extern void add_highpages_with_active_regions(int nid, unsigned long start_pfn,
  * on PREEMPT_RT kmap_atomic() is a wrapper that uses kmap():
  */
 #ifdef CONFIG_PREEMPT_RT
-# define kmap_atomic_prot(page, type, prot)	({ pagefault_disable(); kmap(page); })
+# define kmap_atomic_prot(page, type, prot)	({ pagefault_disable(); kmap_pfn_prot(page_to_pfn(page), prot); })
+# define kmap_atomic_prot_pfn(pfn, type, prot)	({ pagefault_disable(); kmap_pfn_prot(pfn, prot); })
 # define kmap_atomic(page, type)	({ pagefault_disable(); kmap(page); })
 # define kmap_atomic_pfn(pfn, type)	kmap(pfn_to_page(pfn))
-# define kunmap_atomic(kvaddr, type)	do { pagefault_enable(); kunmap_virt(kvaddr); } while(0)
+# define kunmap_atomic(kvaddr, type)	do { kunmap_virt(kvaddr); pagefault_enable(); } while(0)
 # define kmap_atomic_to_page(kvaddr)	kmap_to_page(kvaddr)
 # define kmap_atomic_direct(page, type)	__kmap_atomic_direct(page, type)
 # define kunmap_atomic_direct(kvaddr, type)	__kunmap_atomic(kvaddr, type)
 #else
 # define kmap_atomic_prot(page, type, prot)	__kmap_atomic_prot(page, type, prot)
+# define kmap_atomic_prot_pfn(pfn, type, prot)  __kmap_atomic_prot_pfn(pfn, type, prot)
 # define kmap_atomic(page, type)	__kmap_atomic(page, type)
 # define kmap_atomic_pfn(pfn, type)	__kmap_atomic_pfn(pfn, type)
 # define kunmap_atomic(kvaddr, type)	__kunmap_atomic(kvaddr, type)
diff --git a/arch/x86/mm/highmem_32.c b/arch/x86/mm/highmem_32.c
index dcb1899..b4eb59a 100644
--- a/arch/x86/mm/highmem_32.c
+++ b/arch/x86/mm/highmem_32.c
@@ -19,16 +19,6 @@ void kunmap(struct page *page)
 	kunmap_high(page);
 }
 
-void kunmap_virt(void *ptr)
-{
-	struct page *page;
-
-	if ((unsigned long)ptr < PKMAP_ADDR(0))
-		return;
-	page = pte_page(pkmap_page_table[PKMAP_NR((unsigned long)ptr)]);
-	kunmap(page);
-}
-
 struct page *kmap_to_page(void *ptr)
 {
 	struct page *page;
@@ -70,6 +60,23 @@ void *__kmap_atomic_prot(struct page *page, enum km_type type, pgprot_t prot)
 	return (void *)vaddr;
 }
 
+void *__kmap_atomic_prot_pfn(unsigned long pfn, enum km_type type, pgprot_t prot)
+{
+	enum fixed_addresses idx;
+	unsigned long vaddr;
+
+	preempt_disable();
+	pagefault_disable();
+
+	debug_kmap_atomic(type);
+	idx = type + KM_TYPE_NR * smp_processor_id();
+	vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
+	set_pte(kmap_pte - idx, pfn_pte(pfn, prot));
+	arch_flush_lazy_mmu_mode();
+
+	return (void *)vaddr;
+}
+
 void *__kmap_atomic_direct(struct page *page, enum km_type type)
 {
 	return __kmap_atomic_prot(page, type, kmap_prot);
diff --git a/arch/x86/mm/iomap_32.c b/arch/x86/mm/iomap_32.c
index 715d822..38a1a68 100644
--- a/arch/x86/mm/iomap_32.c
+++ b/arch/x86/mm/iomap_32.c
@@ -55,23 +55,6 @@ iomap_free(resource_size_t base, unsigned long size)
 }
 EXPORT_SYMBOL_GPL(iomap_free);
 
-void *kmap_atomic_prot_pfn(unsigned long pfn, enum km_type type, pgprot_t prot)
-{
-	enum fixed_addresses idx;
-	unsigned long vaddr;
-
-	preempt_disable();
-	pagefault_disable();
-
-	debug_kmap_atomic(type);
-	idx = type + KM_TYPE_NR * smp_processor_id();
-	vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
-	set_pte(kmap_pte - idx, pfn_pte(pfn, prot));
-	arch_flush_lazy_mmu_mode();
-
-	return (void *)vaddr;
-}
-
 /*
  * Map 'pfn' using fixed map 'type' and protections 'prot'
  */
@@ -94,19 +77,6 @@ EXPORT_SYMBOL_GPL(iomap_atomic_prot_pfn);
 void
 iounmap_atomic(void *kvaddr, enum km_type type)
 {
-	unsigned long vaddr = (unsigned long) kvaddr & PAGE_MASK;
-	enum fixed_addresses idx = type + KM_TYPE_NR*smp_processor_id();
-
-	/*
-	 * Force other mappings to Oops if they'll try to access this pte
-	 * without first remap it.  Keeping stale mappings around is a bad idea
-	 * also, in case the page changes cacheability attributes or becomes
-	 * a protected page in a hypervisor.
-	 */
-	if (vaddr == __fix_to_virt(FIX_KMAP_BEGIN+idx))
-		kpte_clear_flush(kmap_pte-idx, vaddr);
-
-	pagefault_enable();
-	preempt_enable();
+	kunmap_atomic(kvaddr, type);
 }
 EXPORT_SYMBOL_GPL(iounmap_atomic);
diff --git a/mm/highmem.c b/mm/highmem.c
index 446b75c..1b534a8 100644
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -66,7 +66,13 @@ unsigned int nr_free_highpages (void)
  *  1 means its free for use - either mapped or not.
  *  n means that there are (n-1) current users of it.
  */
-static atomic_t pkmap_count[LAST_PKMAP];
+
+struct pkmap_state {
+	atomic_t count;
+	int	 pfn;
+};
+
+static struct pkmap_state pkmap[LAST_PKMAP];
 static atomic_t pkmap_hand;
 static atomic_t pkmap_free;
 static atomic_t pkmap_users;
@@ -105,25 +111,26 @@ static DECLARE_WAIT_QUEUE_HEAD(pkmap_wait);
  */
 static int pkmap_try_free(int pos)
 {
-	if (atomic_cmpxchg(&pkmap_count[pos], 1, 0) != 1)
+	if (atomic_cmpxchg(&pkmap[pos].count, 1, 0) != 1)
 		return -1;
 	atomic_dec(&pkmap_free);
 	/*
 	 * TODO: add a young bit to make it CLOCK
 	 */
 	if (!pte_none(pkmap_page_table[pos])) {
-		struct page *page = pte_page(pkmap_page_table[pos]);
 		unsigned long addr = PKMAP_ADDR(pos);
 		pte_t *ptep = &pkmap_page_table[pos];
 
-		VM_BUG_ON(addr != (unsigned long)page_address(page));
+		if (!pkmap[pos].pfn) {
+			struct page *page = pte_page(pkmap_page_table[pos]);
+			VM_BUG_ON(addr != (unsigned long)page_address(page));
+			if (!__set_page_address(page, NULL, pos))
+				BUG();
+			flush_kernel_dcache_page(page);
+		}
 
-		if (!__set_page_address(page, NULL, pos))
-			BUG();
-		flush_kernel_dcache_page(page);
 		pte_clear(&init_mm, addr, ptep);
 
-
 		return 1;
 	}
 
@@ -187,7 +194,7 @@ got_one:
 				continue;
 
 			if (!flush) {
-				atomic_t *counter = &pkmap_count[pos2];
+				atomic_t *counter = &pkmap[pos2].count;
 				VM_BUG_ON(atomic_read(counter) != 0);
 				atomic_set(counter, 2);
 				pkmap_put(counter);
@@ -197,7 +204,7 @@ got_one:
 		flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
 
 		for (i = 0; i < nr; i++) {
-			atomic_t *counter = &pkmap_count[entries[i]];
+			atomic_t *counter = &pkmap[entries[i]].count;
 			VM_BUG_ON(atomic_read(counter) != 0);
 			atomic_set(counter, 2);
 			pkmap_put(counter);
@@ -207,32 +214,51 @@ got_one:
 	return pos;
 }
 
-static unsigned long pkmap_insert(struct page *page)
+static unsigned long pkmap_insert(unsigned long pfn, pgprot_t prot)
 {
 	int pos = pkmap_get_free();
 	unsigned long vaddr = PKMAP_ADDR(pos);
 	pte_t *ptep = &pkmap_page_table[pos];
-	pte_t entry = mk_pte(page, kmap_prot);
-	atomic_t *counter = &pkmap_count[pos];
+	pte_t entry = pfn_pte(pfn, prot);
+	atomic_t *counter = &pkmap[pos].count;
 
 	VM_BUG_ON(atomic_read(counter) != 0);
-
 	set_pte_at(&init_mm, vaddr, ptep, entry);
-	if (unlikely(!__set_page_address(page, (void *)vaddr, pos))) {
+
+	pkmap[pos].pfn =
+		!(pgprot_val(prot) == pgprot_val(kmap_prot) && pfn_valid(pfn));
+
+	if (!pkmap[pos].pfn) {
+		struct page *page = pfn_to_page(pfn);
+
+		if (unlikely(!__set_page_address(page, (void *)vaddr, pos))) {
+			/*
+			 * concurrent pkmap_inserts for this page -
+			 * the other won the race, release this entry.
+			 *
+			 * we can still clear the pte without a tlb flush since
+			 * it couldn't have been used yet.
+			 */
+			pte_clear(&init_mm, vaddr, ptep);
+			VM_BUG_ON(atomic_read(counter) != 0);
+			atomic_set(counter, 2);
+			pkmap_put(counter);
+			return 0;
+		}
+	} else {
+#ifdef ARCH_NEEDS_KMAP_HIGH_GET
 		/*
-		 * concurrent pkmap_inserts for this page -
-		 * the other won the race, release this entry.
+		 * non-default prot and pure pfn memory doesn't
+		 * get map deduplication, nor a working page_address
 		 *
-		 * we can still clear the pte without a tlb flush since
-		 * it couldn't have been used yet.
+		 * this also makes it incompatible with
+		 * ARCH_NEEDS_KMAP_HIGH_GET
 		 */
-		pte_clear(&init_mm, vaddr, ptep);
-		VM_BUG_ON(atomic_read(counter) != 0);
-		atomic_set(counter, 2);
-		pkmap_put(counter);
-		vaddr = 0;
-	} else
-		atomic_set(counter, 2);
+		BUG();
+#endif
+	}
+
+	atomic_set(counter, 2);
 
 	return vaddr;
 }
@@ -313,20 +339,17 @@ static void kunmap_account(void)
 	wake_up(&pkmap_wait);
 }
 
-void *kmap_high(struct page *page)
+void *kmap_get(struct page *page)
 {
 	unsigned long vaddr;
-
-
-	kmap_account();
 again:
 	vaddr = (unsigned long)page_address(page);
 	if (vaddr) {
-		atomic_t *counter = &pkmap_count[PKMAP_NR(vaddr)];
+		atomic_t *counter = &pkmap[PKMAP_NR(vaddr)].count;
 		if (atomic_inc_not_zero(counter)) {
 			/*
-			 * atomic_inc_not_zero implies a (memory) barrier on success
-			 * so page address will be reloaded.
+			 * atomic_inc_not_zero implies a (memory) barrier on
+			 * success so page address will be reloaded.
 			 */
 			unsigned long vaddr2 = (unsigned long)page_address(page);
 			if (likely(vaddr == vaddr2))
@@ -341,19 +364,49 @@ again:
 			 * reused.
 			 */
 			pkmap_put(counter);
-			goto again;
 		}
+		goto again;
 	}
+	return (void *)vaddr;
+}
 
-	vaddr = pkmap_insert(page);
-	if (!vaddr)
-		goto again;
+void *kmap_high(struct page *page)
+{
+	unsigned long vaddr;
+
+	kmap_account();
+
+again:
+	vaddr = (unsigned long)kmap_get(page);
+	if (!vaddr) {
+		vaddr = pkmap_insert(page_to_pfn(page), kmap_prot);
+		if (!vaddr)
+			goto again;
+	}
 
 	return (void *)vaddr;
 }
 
 EXPORT_SYMBOL(kmap_high);
 
+void *kmap_pfn_prot(unsigned long pfn, pgprot_t prot)
+{
+	unsigned long vaddr;
+
+	if (pgprot_val(prot) == pgprot_val(kmap_prot) &&
+			pfn_valid(pfn) && PageHighMem(pfn_to_page(pfn)))
+		return kmap_high(pfn_to_page(pfn));
+
+	kmap_account();
+
+	vaddr = pkmap_insert(pfn, prot);
+	BUG_ON(!vaddr);
+
+	return (void *)vaddr;
+}
+
+EXPORT_SYMBOL(kmap_pfn_prot);
+
 #ifdef ARCH_NEEDS_KMAP_HIGH_GET
 /**
  * kmap_high_get - pin a highmem page into memory
@@ -370,21 +423,26 @@ void *kmap_high_get(struct page *page)
 	unsigned long vaddr, flags;
 
 	lock_kmap_any(flags);
-	vaddr = (unsigned long)page_address(page);
-	if (vaddr) {
-		BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 1);
-		pkmap_count[PKMAP_NR(vaddr)]++;
-	}
+	vaddr = (unsigned long)kmap_get(page);
 	unlock_kmap_any(flags);
-	return (void*) vaddr;
+	return (void *)vaddr;
 }
 #endif
 
- void kunmap_high(struct page *page)
+void kunmap_virt(void *ptr)
+{
+	unsigned long vaddr = (unsigned long)ptr;
+	if (vaddr < PKMAP_ADDR(0) || vaddr >= PKMAP_ADDR(LAST_PKMAP))
+		return;
+	pkmap_put(&pkmap[PKMAP_NR(vaddr)].count);
+	kunmap_account();
+}
+
+void kunmap_high(struct page *page)
 {
 	unsigned long vaddr = (unsigned long)page_address(page);
 	BUG_ON(!vaddr);
-	pkmap_put(&pkmap_count[PKMAP_NR(vaddr)]);
+	pkmap_put(&pkmap[PKMAP_NR(vaddr)].count);
 	kunmap_account();
 }
 
@@ -539,8 +597,8 @@ void __init page_address_init(void)
 #ifdef CONFIG_HIGHMEM
 	int i;
 
-	for (i = 0; i < ARRAY_SIZE(pkmap_count); i++)
-		atomic_set(&pkmap_count[i], 1);
+	for (i = 0; i < ARRAY_SIZE(pkmap); i++)
+		atomic_set(&pkmap[i].count, 1);
 	atomic_set(&pkmap_hand, 0);
 	atomic_set(&pkmap_free, LAST_PKMAP);
 	atomic_set(&pkmap_users, 0);


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