Re: [PATCH kernel 2/9] powerpc/mmu: Add real mode support for IOMMU preregistered memory

[David Gibson]

On Mon, Mar 07, 2016 at 02:41:10PM +1100, Alexey Kardashevskiy wrote:
> This makes mm_iommu_lookup() able to work in realmode by replacing
> list_for_each_entry_rcu() (which can do debug stuff which can fail in
> real mode) with list_for_each_entry_lockless().
> 
> This adds realmode version of mm_iommu_ua_to_hpa() which adds
> explicit vmalloc'd-to-linear address conversion.
> Unlike mm_iommu_ua_to_hpa(), mm_iommu_rm_ua_to_hpa() can fail.
> 
> This changes mm_iommu_preregistered() to receive @mm as in real mode
> @current does not always have a correct pointer.

So, I'd generally expect a parameter called @mm to be an mm_struct *,
not a mm_context_t.

> 
> This adds realmode version of mm_iommu_lookup() which receives @mm
> (for the same reason as for mm_iommu_preregistered()) and uses
> lockless version of list_for_each_entry_rcu().
> 
> Signed-off-by: Alexey Kardashevskiy 



> ---
>  arch/powerpc/include/asm/mmu_context.h |  6 -
>  arch/powerpc/mm/mmu_context_iommu.c| 45 
> ++
>  2 files changed, 45 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/mmu_context.h 
> b/arch/powerpc/include/asm/mmu_context.h
> index 878c277..3ba652a 100644
> --- a/arch/powerpc/include/asm/mmu_context.h
> +++ b/arch/powerpc/include/asm/mmu_context.h
> @@ -18,7 +18,7 @@ extern void destroy_context(struct mm_struct *mm);
>  #ifdef CONFIG_SPAPR_TCE_IOMMU
>  struct mm_iommu_table_group_mem_t;
>  
> -extern bool mm_iommu_preregistered(void);
> +extern bool mm_iommu_preregistered(mm_context_t *mm);
>  extern long mm_iommu_get(unsigned long ua, unsigned long entries,
>   struct mm_iommu_table_group_mem_t **pmem);
>  extern long mm_iommu_put(struct mm_iommu_table_group_mem_t *mem);
> @@ -26,10 +26,14 @@ extern void mm_iommu_init(mm_context_t *ctx);
>  extern void mm_iommu_cleanup(mm_context_t *ctx);
>  extern struct mm_iommu_table_group_mem_t *mm_iommu_lookup(unsigned long ua,
>   unsigned long size);
> +extern struct mm_iommu_table_group_mem_t *mm_iommu_lookup_rm(mm_context_t 
> *mm,
> + unsigned long ua, unsigned long size);
>  extern struct mm_iommu_table_group_mem_t *mm_iommu_find(unsigned long ua,
>   unsigned long entries);
>  extern long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
>   unsigned long ua, unsigned long *hpa);
> +extern long mm_iommu_rm_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
> + unsigned long ua, unsigned long *hpa);
>  extern long mm_iommu_mapped_inc(struct mm_iommu_table_group_mem_t *mem);
>  extern void mm_iommu_mapped_dec(struct mm_iommu_table_group_mem_t *mem);
>  #endif
> diff --git a/arch/powerpc/mm/mmu_context_iommu.c 
> b/arch/powerpc/mm/mmu_context_iommu.c
> index da6a216..aa1565d 100644
> --- a/arch/powerpc/mm/mmu_context_iommu.c
> +++ b/arch/powerpc/mm/mmu_context_iommu.c
> @@ -63,12 +63,9 @@ static long mm_iommu_adjust_locked_vm(struct mm_struct *mm,
>   return ret;
>  }
>  
> -bool mm_iommu_preregistered(void)
> +bool mm_iommu_preregistered(mm_context_t *mm)
>  {
> - if (!current || !current->mm)
> - return false;
> -
> - return !list_empty(>mm->context.iommu_group_mem_list);
> + return !list_empty(>iommu_group_mem_list);
>  }
>  EXPORT_SYMBOL_GPL(mm_iommu_preregistered);
>  
> @@ -231,6 +228,24 @@ unlock_exit:
>  }
>  EXPORT_SYMBOL_GPL(mm_iommu_put);
>  
> +struct mm_iommu_table_group_mem_t *mm_iommu_lookup_rm(mm_context_t *mm,
> + unsigned long ua, unsigned long size)
> +{
> + struct mm_iommu_table_group_mem_t *mem, *ret = NULL;

I think you could do with a comment here explaining why the lockless
traversal is safe.

> + list_for_each_entry_lockless(mem, >iommu_group_mem_list, next) {
> + if ((mem->ua <= ua) &&
> + (ua + size <= mem->ua +
> +  (mem->entries << PAGE_SHIFT))) {
> + ret = mem;
> + break;
> + }
> + }
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(mm_iommu_lookup_rm);
> +
>  struct mm_iommu_table_group_mem_t *mm_iommu_lookup(unsigned long ua,
>   unsigned long size)
>  {
> @@ -284,6 +299,26 @@ long mm_iommu_ua_to_hpa(struct 
> mm_iommu_table_group_mem_t *mem,
>  }
>  EXPORT_SYMBOL_GPL(mm_iommu_ua_to_hpa);
>  
> +long mm_iommu_rm_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
> + unsigned long ua, unsigned long *hpa)
> +{
> + const long entry = (ua - mem->ua) >> PAGE_SHIFT;
> + void *va = >hpas[entry];
> + unsigned long *ra;
> +
> + if (entry >= mem->entries)
> + return -EFAULT;
> +
> + ra = (void *) vmalloc_to_phys(va);
> + if (!ra)
> + return -EFAULT;
> +
> + *hpa = *ra | (ua & ~PAGE_MASK);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(mm_iommu_rm_ua_to_hpa);
> +
>  long mm_iommu_mapped_inc(struct mm_iommu_table_group_mem_t *mem)
>  {
>   if 

[PATCH kernel 2/9] powerpc/mmu: Add real mode support for IOMMU preregistered memory

[Alexey Kardashevskiy]

This makes mm_iommu_lookup() able to work in realmode by replacing
list_for_each_entry_rcu() (which can do debug stuff which can fail in
real mode) with list_for_each_entry_lockless().

This adds realmode version of mm_iommu_ua_to_hpa() which adds
explicit vmalloc'd-to-linear address conversion.
Unlike mm_iommu_ua_to_hpa(), mm_iommu_rm_ua_to_hpa() can fail.

This changes mm_iommu_preregistered() to receive @mm as in real mode
@current does not always have a correct pointer.

This adds realmode version of mm_iommu_lookup() which receives @mm
(for the same reason as for mm_iommu_preregistered()) and uses
lockless version of list_for_each_entry_rcu().

Signed-off-by: Alexey Kardashevskiy 
---
 arch/powerpc/include/asm/mmu_context.h |  6 -
 arch/powerpc/mm/mmu_context_iommu.c| 45 ++
 2 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/include/asm/mmu_context.h 
b/arch/powerpc/include/asm/mmu_context.h
index 878c277..3ba652a 100644
--- a/arch/powerpc/include/asm/mmu_context.h
+++ b/arch/powerpc/include/asm/mmu_context.h
@@ -18,7 +18,7 @@ extern void destroy_context(struct mm_struct *mm);
 #ifdef CONFIG_SPAPR_TCE_IOMMU
 struct mm_iommu_table_group_mem_t;
 
-extern bool mm_iommu_preregistered(void);
+extern bool mm_iommu_preregistered(mm_context_t *mm);
 extern long mm_iommu_get(unsigned long ua, unsigned long entries,
struct mm_iommu_table_group_mem_t **pmem);
 extern long mm_iommu_put(struct mm_iommu_table_group_mem_t *mem);
@@ -26,10 +26,14 @@ extern void mm_iommu_init(mm_context_t *ctx);
 extern void mm_iommu_cleanup(mm_context_t *ctx);
 extern struct mm_iommu_table_group_mem_t *mm_iommu_lookup(unsigned long ua,
unsigned long size);
+extern struct mm_iommu_table_group_mem_t *mm_iommu_lookup_rm(mm_context_t *mm,
+   unsigned long ua, unsigned long size);
 extern struct mm_iommu_table_group_mem_t *mm_iommu_find(unsigned long ua,
unsigned long entries);
 extern long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
unsigned long ua, unsigned long *hpa);
+extern long mm_iommu_rm_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
+   unsigned long ua, unsigned long *hpa);
 extern long mm_iommu_mapped_inc(struct mm_iommu_table_group_mem_t *mem);
 extern void mm_iommu_mapped_dec(struct mm_iommu_table_group_mem_t *mem);
 #endif
diff --git a/arch/powerpc/mm/mmu_context_iommu.c 
b/arch/powerpc/mm/mmu_context_iommu.c
index da6a216..aa1565d 100644
--- a/arch/powerpc/mm/mmu_context_iommu.c
+++ b/arch/powerpc/mm/mmu_context_iommu.c
@@ -63,12 +63,9 @@ static long mm_iommu_adjust_locked_vm(struct mm_struct *mm,
return ret;
 }
 
-bool mm_iommu_preregistered(void)
+bool mm_iommu_preregistered(mm_context_t *mm)
 {
-   if (!current || !current->mm)
-   return false;
-
-   return !list_empty(>mm->context.iommu_group_mem_list);
+   return !list_empty(>iommu_group_mem_list);
 }
 EXPORT_SYMBOL_GPL(mm_iommu_preregistered);
 
@@ -231,6 +228,24 @@ unlock_exit:
 }
 EXPORT_SYMBOL_GPL(mm_iommu_put);
 
+struct mm_iommu_table_group_mem_t *mm_iommu_lookup_rm(mm_context_t *mm,
+   unsigned long ua, unsigned long size)
+{
+   struct mm_iommu_table_group_mem_t *mem, *ret = NULL;
+
+   list_for_each_entry_lockless(mem, >iommu_group_mem_list, next) {
+   if ((mem->ua <= ua) &&
+   (ua + size <= mem->ua +
+(mem->entries << PAGE_SHIFT))) {
+   ret = mem;
+   break;
+   }
+   }
+
+   return ret;
+}
+EXPORT_SYMBOL_GPL(mm_iommu_lookup_rm);
+
 struct mm_iommu_table_group_mem_t *mm_iommu_lookup(unsigned long ua,
unsigned long size)
 {
@@ -284,6 +299,26 @@ long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t 
*mem,
 }
 EXPORT_SYMBOL_GPL(mm_iommu_ua_to_hpa);
 
+long mm_iommu_rm_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
+   unsigned long ua, unsigned long *hpa)
+{
+   const long entry = (ua - mem->ua) >> PAGE_SHIFT;
+   void *va = >hpas[entry];
+   unsigned long *ra;
+
+   if (entry >= mem->entries)
+   return -EFAULT;
+
+   ra = (void *) vmalloc_to_phys(va);
+   if (!ra)
+   return -EFAULT;
+
+   *hpa = *ra | (ua & ~PAGE_MASK);
+
+   return 0;
+}
+EXPORT_SYMBOL_GPL(mm_iommu_rm_ua_to_hpa);
+
 long mm_iommu_mapped_inc(struct mm_iommu_table_group_mem_t *mem)
 {
if (atomic64_inc_not_zero(>mapped))
-- 
2.5.0.rc3

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