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Subject[patch 1/3] atomic copy_*_user() infrastructure


The patch implements the atomic copy_*_user() function.

If the kernel takes a pagefault while running copy_*_user() in an
atomic region, the copy_*_user() will fail (return a short value).

And with this patch, holding an atomic kmap() puts the CPU into an
atomic region.

- Increment preempt_count() in kmap_atomic() regardless of the
setting of CONFIG_PREEMPT. The pagefault handler recognises this as
an atomic region and refuses to service the fault. copy_*_user will
return a non-zero value.

- Attempts to propagate the in_atomic() predicate to all the other
highmem-capable architectures' pagefault handlers. But the code is
only tested on x86.

- Fixed a PPC bug in kunmap_atomic(): it forgot to reenable
preemption if HIGHMEM_DEBUG is turned on.

- Fixed a sparc bug in kunmap_atomic(): it forgot to reenable
preemption all the time, for non-fixmap pages.

- Fix an error in <linux/highmem.h> - in the CONFIG_HIGHMEM=n case,
kunmap_atomic() takes an address, not a page *.



arch/ppc/mm/fault.c | 2 +-
arch/sparc/mm/fault.c | 2 +-
include/asm-i386/highmem.h | 6 +++---
include/asm-ppc/hardirq.h | 2 ++
include/asm-ppc/highmem.h | 6 +++++-
include/asm-sparc/hardirq.h | 6 ++++++
include/asm-sparc/highmem.h | 6 +++++-
include/linux/highmem.h | 4 ++--
8 files changed, 25 insertions(+), 9 deletions(-)

--- 2.5.33/include/asm-i386/highmem.h~copy_user_atomic Thu Sep 5 00:44:46 2002
+++ 2.5.33-akpm/include/asm-i386/highmem.h Thu Sep 5 00:44:46 2002
@@ -81,7 +81,7 @@ static inline void *kmap_atomic(struct p
enum fixed_addresses idx;
unsigned long vaddr;

- preempt_disable();
+ inc_preempt_count();
if (page < highmem_start_page)
return page_address(page);

@@ -104,7 +104,7 @@ static inline void kunmap_atomic(void *k
enum fixed_addresses idx = type + KM_TYPE_NR*smp_processor_id();

if (vaddr < FIXADDR_START) { // FIXME
- preempt_enable();
+ dec_preempt_count();
return;
}

@@ -119,7 +119,7 @@ static inline void kunmap_atomic(void *k
__flush_tlb_one(vaddr);
#endif

- preempt_enable();
+ dec_preempt_count();
}

#endif /* __KERNEL__ */
--- 2.5.33/include/asm-ppc/highmem.h~copy_user_atomic Thu Sep 5 00:44:46 2002
+++ 2.5.33-akpm/include/asm-ppc/highmem.h Thu Sep 5 00:44:46 2002
@@ -88,6 +88,7 @@ static inline void *kmap_atomic(struct p
unsigned int idx;
unsigned long vaddr;

+ inc_preempt_count();
if (page < highmem_start_page)
return page_address(page);

@@ -109,8 +110,10 @@ static inline void kunmap_atomic(void *k
unsigned long vaddr = (unsigned long) kvaddr & PAGE_MASK;
unsigned int idx = type + KM_TYPE_NR*smp_processor_id();

- if (vaddr < KMAP_FIX_BEGIN) // FIXME
+ if (vaddr < KMAP_FIX_BEGIN) { // FIXME
+ dec_preempt_count();
return;
+ }

if (vaddr != KMAP_FIX_BEGIN + idx * PAGE_SIZE)
BUG();
@@ -122,6 +125,7 @@ static inline void kunmap_atomic(void *k
pte_clear(kmap_pte+idx);
flush_tlb_page(0, vaddr);
#endif
+ dec_preempt_count();
}

#endif /* __KERNEL__ */
--- 2.5.33/include/asm-sparc/highmem.h~copy_user_atomic Thu Sep 5 00:44:46 2002
+++ 2.5.33-akpm/include/asm-sparc/highmem.h Thu Sep 5 00:44:46 2002
@@ -83,6 +83,7 @@ static inline void *kmap_atomic(struct p
unsigned long idx;
unsigned long vaddr;

+ inc_preempt_count();
if (page < highmem_start_page)
return page_address(page);

@@ -116,8 +117,10 @@ static inline void kunmap_atomic(void *k
unsigned long vaddr = (unsigned long) kvaddr;
unsigned long idx = type + KM_TYPE_NR*smp_processor_id();

- if (vaddr < FIX_KMAP_BEGIN) // FIXME
+ if (vaddr < FIX_KMAP_BEGIN) { // FIXME
+ dec_preempt_count();
return;
+ }

if (vaddr != FIX_KMAP_BEGIN + idx * PAGE_SIZE)
BUG();
@@ -142,6 +145,7 @@ static inline void kunmap_atomic(void *k
flush_tlb_all();
#endif
#endif
+ dec_preempt_count();
}

#endif /* __KERNEL__ */
--- 2.5.33/arch/sparc/mm/fault.c~copy_user_atomic Thu Sep 5 00:44:46 2002
+++ 2.5.33-akpm/arch/sparc/mm/fault.c Thu Sep 5 00:44:46 2002
@@ -233,7 +233,7 @@ asmlinkage void do_sparc_fault(struct pt
* If we're in an interrupt or have no user
* context, we must not take the fault..
*/
- if (in_interrupt() || !mm)
+ if (in_atomic() || !mm)
goto no_context;

down_read(&mm->mmap_sem);
--- 2.5.33/arch/ppc/mm/fault.c~copy_user_atomic Thu Sep 5 00:44:46 2002
+++ 2.5.33-akpm/arch/ppc/mm/fault.c Thu Sep 5 00:44:46 2002
@@ -102,7 +102,7 @@ void do_page_fault(struct pt_regs *regs,
#endif /* !CONFIG_4xx */
#endif /* CONFIG_XMON || CONFIG_KGDB */

- if (in_interrupt() || mm == NULL) {
+ if (in_atomic() || mm == NULL) {
bad_page_fault(regs, address, SIGSEGV);
return;
}
--- 2.5.33/include/asm-sparc/hardirq.h~copy_user_atomic Thu Sep 5 00:44:46 2002
+++ 2.5.33-akpm/include/asm-sparc/hardirq.h Thu Sep 5 00:44:46 2002
@@ -113,6 +113,12 @@ do {
#define irq_exit() br_read_unlock(BR_GLOBALIRQ_LOCK)
#endif

+#if CONFIG_PREEMPT
+# define in_atomic() (preempt_count() != kernel_locked())
+#else
+# define in_atomic() (preempt_count() != 0)
+#endif
+
#ifndef CONFIG_SMP

#define synchronize_irq() barrier()
--- 2.5.33/include/asm-ppc/hardirq.h~copy_user_atomic Thu Sep 5 00:44:46 2002
+++ 2.5.33-akpm/include/asm-ppc/hardirq.h Thu Sep 5 00:44:46 2002
@@ -85,8 +85,10 @@ typedef struct {
#define irq_enter() (preempt_count() += HARDIRQ_OFFSET)

#if CONFIG_PREEMPT
+# define in_atomic() (preempt_count() != kernel_locked())
# define IRQ_EXIT_OFFSET (HARDIRQ_OFFSET-1)
#else
+# define in_atomic() (preempt_count() != 0)
# define IRQ_EXIT_OFFSET HARDIRQ_OFFSET
#endif
#define irq_exit() \
--- 2.5.33/include/linux/highmem.h~copy_user_atomic Thu Sep 5 00:44:46 2002
+++ 2.5.33-akpm/include/linux/highmem.h Thu Sep 5 00:44:46 2002
@@ -24,8 +24,8 @@ static inline void *kmap(struct page *pa

#define kunmap(page) do { (void) (page); } while (0)

-#define kmap_atomic(page,idx) kmap(page)
-#define kunmap_atomic(page,idx) kunmap(page)
+#define kmap_atomic(page, idx) page_address(page)
+#define kunmap_atomic(addr, idx) do { } while (0)

#endif /* CONFIG_HIGHMEM */

.
-
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