exec: Add lock parameter to qemu_ram_ptr_length

[Qemu-devel] [PATCH for-2.10] exec: Add lock parameter to qemu_ram_ptr_length

Posted by Anthony PERARD 6 years, 9 months ago

Commit 04bf2526ce87f21b32c9acba1c5518708c243ad0 (exec: use
qemu_ram_ptr_length to access guest ram) start using qemu_ram_ptr_length
instead of qemu_map_ram_ptr, but when used with Xen, the behavior of
both function is different. They both call xen_map_cache, but one with
"lock", meaning the mapping of guest memory is never released
implicitly, and the second one without, which means, mapping can be
release later, when needed.

In the context of address_space_{read,write}_continue, the ptr to those
mapping should not be locked because it is used immediatly and never
used again.

The lock parameter make it explicit in which context qemu_ram_ptr_length
is called.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
---
 exec.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/exec.c b/exec.c
index 01ac21e3cd..63508cd35e 100644
--- a/exec.c
+++ b/exec.c
@@ -2203,7 +2203,7 @@ void *qemu_map_ram_ptr(RAMBlock *ram_block, ram_addr_t addr)
  * Called within RCU critical section.
  */
 static void *qemu_ram_ptr_length(RAMBlock *ram_block, ram_addr_t addr,
-                                 hwaddr *size)
+                                 hwaddr *size, bool lock)
 {
     RAMBlock *block = ram_block;
     if (*size == 0) {
@@ -2222,10 +2222,10 @@ static void *qemu_ram_ptr_length(RAMBlock *ram_block, ram_addr_t addr,
          * In that case just map the requested area.
          */
         if (block->offset == 0) {
-            return xen_map_cache(addr, *size, 1, true);
+            return xen_map_cache(addr, *size, lock ? 1 : 0, lock);
         }
 
-        block->host = xen_map_cache(block->offset, block->max_length, 1, true);
+        block->host = xen_map_cache(block->offset, block->max_length, 1, lock);
     }
 
     return ramblock_ptr(block, addr);
@@ -2947,7 +2947,7 @@ static MemTxResult address_space_write_continue(AddressSpace *as, hwaddr addr,
             }
         } else {
             /* RAM case */
-            ptr = qemu_ram_ptr_length(mr->ram_block, addr1, &l);
+            ptr = qemu_ram_ptr_length(mr->ram_block, addr1, &l, false);
             memcpy(ptr, buf, l);
             invalidate_and_set_dirty(mr, addr1, l);
         }
@@ -3038,7 +3038,7 @@ MemTxResult address_space_read_continue(AddressSpace *as, hwaddr addr,
             }
         } else {
             /* RAM case */
-            ptr = qemu_ram_ptr_length(mr->ram_block, addr1, &l);
+            ptr = qemu_ram_ptr_length(mr->ram_block, addr1, &l, false);
             memcpy(buf, ptr, l);
         }
 
@@ -3349,7 +3349,7 @@ void *address_space_map(AddressSpace *as,
 
     memory_region_ref(mr);
     *plen = address_space_extend_translation(as, addr, len, mr, xlat, l, is_write);
-    ptr = qemu_ram_ptr_length(mr->ram_block, xlat, plen);
+    ptr = qemu_ram_ptr_length(mr->ram_block, xlat, plen, true);
     rcu_read_unlock();
 
     return ptr;
-- 
Anthony PERARD

Re: [Qemu-devel] [PATCH for-2.10] exec: Add lock parameter to qemu_ram_ptr_length

Posted by Paolo Bonzini 6 years, 9 months ago

On 26/07/2017 18:53, Anthony PERARD wrote:
> Commit 04bf2526ce87f21b32c9acba1c5518708c243ad0 (exec: use
> qemu_ram_ptr_length to access guest ram) start using qemu_ram_ptr_length
> instead of qemu_map_ram_ptr, but when used with Xen, the behavior of
> both function is different. They both call xen_map_cache, but one with
> "lock", meaning the mapping of guest memory is never released
> implicitly, and the second one without, which means, mapping can be
> release later, when needed.
> 
> In the context of address_space_{read,write}_continue, the ptr to those
> mapping should not be locked because it is used immediatly and never
> used again.
> 
> The lock parameter make it explicit in which context qemu_ram_ptr_length
> is called.
> 
> Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>

Thanks for implementing it.  I'll send a pull request for rc1.

Paolo

> ---
>  exec.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index 01ac21e3cd..63508cd35e 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2203,7 +2203,7 @@ void *qemu_map_ram_ptr(RAMBlock *ram_block, ram_addr_t addr)
>   * Called within RCU critical section.
>   */
>  static void *qemu_ram_ptr_length(RAMBlock *ram_block, ram_addr_t addr,
> -                                 hwaddr *size)
> +                                 hwaddr *size, bool lock)
>  {
>      RAMBlock *block = ram_block;
>      if (*size == 0) {
> @@ -2222,10 +2222,10 @@ static void *qemu_ram_ptr_length(RAMBlock *ram_block, ram_addr_t addr,
>           * In that case just map the requested area.
>           */
>          if (block->offset == 0) {
> -            return xen_map_cache(addr, *size, 1, true);
> +            return xen_map_cache(addr, *size, lock ? 1 : 0, lock);
>          }
>  
> -        block->host = xen_map_cache(block->offset, block->max_length, 1, true);
> +        block->host = xen_map_cache(block->offset, block->max_length, 1, lock);
>      }
>  
>      return ramblock_ptr(block, addr);
> @@ -2947,7 +2947,7 @@ static MemTxResult address_space_write_continue(AddressSpace *as, hwaddr addr,
>              }
>          } else {
>              /* RAM case */
> -            ptr = qemu_ram_ptr_length(mr->ram_block, addr1, &l);
> +            ptr = qemu_ram_ptr_length(mr->ram_block, addr1, &l, false);
>              memcpy(ptr, buf, l);
>              invalidate_and_set_dirty(mr, addr1, l);
>          }
> @@ -3038,7 +3038,7 @@ MemTxResult address_space_read_continue(AddressSpace *as, hwaddr addr,
>              }
>          } else {
>              /* RAM case */
> -            ptr = qemu_ram_ptr_length(mr->ram_block, addr1, &l);
> +            ptr = qemu_ram_ptr_length(mr->ram_block, addr1, &l, false);
>              memcpy(buf, ptr, l);
>          }
>  
> @@ -3349,7 +3349,7 @@ void *address_space_map(AddressSpace *as,
>  
>      memory_region_ref(mr);
>      *plen = address_space_extend_translation(as, addr, len, mr, xlat, l, is_write);
> -    ptr = qemu_ram_ptr_length(mr->ram_block, xlat, plen);
> +    ptr = qemu_ram_ptr_length(mr->ram_block, xlat, plen, true);
>      rcu_read_unlock();
>  
>      return ptr;
>

Re: [Qemu-devel] [PATCH for-2.10] exec: Add lock parameter to qemu_ram_ptr_length

Posted by Stefano Stabellini 6 years, 9 months ago

On Wed, 26 Jul 2017, Anthony PERARD wrote:
> Commit 04bf2526ce87f21b32c9acba1c5518708c243ad0 (exec: use
> qemu_ram_ptr_length to access guest ram) start using qemu_ram_ptr_length
> instead of qemu_map_ram_ptr, but when used with Xen, the behavior of
> both function is different. They both call xen_map_cache, but one with
> "lock", meaning the mapping of guest memory is never released
> implicitly, and the second one without, which means, mapping can be
> release later, when needed.
> 
> In the context of address_space_{read,write}_continue, the ptr to those
> mapping should not be locked because it is used immediatly and never
> used again.
> 
> The lock parameter make it explicit in which context qemu_ram_ptr_length
> is called.
> 
> Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>

Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>


> ---
>  exec.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index 01ac21e3cd..63508cd35e 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2203,7 +2203,7 @@ void *qemu_map_ram_ptr(RAMBlock *ram_block, ram_addr_t addr)
>   * Called within RCU critical section.
>   */
>  static void *qemu_ram_ptr_length(RAMBlock *ram_block, ram_addr_t addr,
> -                                 hwaddr *size)
> +                                 hwaddr *size, bool lock)
>  {
>      RAMBlock *block = ram_block;
>      if (*size == 0) {
> @@ -2222,10 +2222,10 @@ static void *qemu_ram_ptr_length(RAMBlock *ram_block, ram_addr_t addr,
>           * In that case just map the requested area.
>           */
>          if (block->offset == 0) {
> -            return xen_map_cache(addr, *size, 1, true);
> +            return xen_map_cache(addr, *size, lock ? 1 : 0, lock);
>          }
>  
> -        block->host = xen_map_cache(block->offset, block->max_length, 1, true);
> +        block->host = xen_map_cache(block->offset, block->max_length, 1, lock);
>      }
>  
>      return ramblock_ptr(block, addr);
> @@ -2947,7 +2947,7 @@ static MemTxResult address_space_write_continue(AddressSpace *as, hwaddr addr,
>              }
>          } else {
>              /* RAM case */
> -            ptr = qemu_ram_ptr_length(mr->ram_block, addr1, &l);
> +            ptr = qemu_ram_ptr_length(mr->ram_block, addr1, &l, false);
>              memcpy(ptr, buf, l);
>              invalidate_and_set_dirty(mr, addr1, l);
>          }
> @@ -3038,7 +3038,7 @@ MemTxResult address_space_read_continue(AddressSpace *as, hwaddr addr,
>              }
>          } else {
>              /* RAM case */
> -            ptr = qemu_ram_ptr_length(mr->ram_block, addr1, &l);
> +            ptr = qemu_ram_ptr_length(mr->ram_block, addr1, &l, false);
>              memcpy(buf, ptr, l);
>          }
>  
> @@ -3349,7 +3349,7 @@ void *address_space_map(AddressSpace *as,
>  
>      memory_region_ref(mr);
>      *plen = address_space_extend_translation(as, addr, len, mr, xlat, l, is_write);
> -    ptr = qemu_ram_ptr_length(mr->ram_block, xlat, plen);
> +    ptr = qemu_ram_ptr_length(mr->ram_block, xlat, plen, true);
>      rcu_read_unlock();
>  
>      return ptr;
> -- 
> Anthony PERARD
>

Re: [Qemu-devel] [PATCH for-2.10] exec: Add lock parameter to qemu_ram_ptr_length

Posted by Paolo Bonzini 6 years, 9 months ago

On 26/07/2017 18:53, Anthony PERARD wrote:
> Commit 04bf2526ce87f21b32c9acba1c5518708c243ad0 (exec: use
> qemu_ram_ptr_length to access guest ram) start using qemu_ram_ptr_length
> instead of qemu_map_ram_ptr, but when used with Xen, the behavior of
> both function is different. They both call xen_map_cache, but one with
> "lock", meaning the mapping of guest memory is never released
> implicitly, and the second one without, which means, mapping can be
> release later, when needed.
> 
> In the context of address_space_{read,write}_continue, the ptr to those
> mapping should not be locked because it is used immediatly and never
> used again.
> 
> The lock parameter make it explicit in which context qemu_ram_ptr_length
> is called.
> 
> Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
> ---
>  exec.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index 01ac21e3cd..63508cd35e 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2203,7 +2203,7 @@ void *qemu_map_ram_ptr(RAMBlock *ram_block, ram_addr_t addr)
>   * Called within RCU critical section.
>   */
>  static void *qemu_ram_ptr_length(RAMBlock *ram_block, ram_addr_t addr,
> -                                 hwaddr *size)
> +                                 hwaddr *size, bool lock)
>  {
>      RAMBlock *block = ram_block;
>      if (*size == 0) {
> @@ -2222,10 +2222,10 @@ static void *qemu_ram_ptr_length(RAMBlock *ram_block, ram_addr_t addr,
>           * In that case just map the requested area.
>           */
>          if (block->offset == 0) {
> -            return xen_map_cache(addr, *size, 1, true);
> +            return xen_map_cache(addr, *size, lock ? 1 : 0, lock);
>          }
>  
> -        block->host = xen_map_cache(block->offset, block->max_length, 1, true);
> +        block->host = xen_map_cache(block->offset, block->max_length, 1, lock);
>      }
>  
>      return ramblock_ptr(block, addr);
> @@ -2947,7 +2947,7 @@ static MemTxResult address_space_write_continue(AddressSpace *as, hwaddr addr,
>              }
>          } else {
>              /* RAM case */
> -            ptr = qemu_ram_ptr_length(mr->ram_block, addr1, &l);
> +            ptr = qemu_ram_ptr_length(mr->ram_block, addr1, &l, false);
>              memcpy(ptr, buf, l);
>              invalidate_and_set_dirty(mr, addr1, l);
>          }
> @@ -3038,7 +3038,7 @@ MemTxResult address_space_read_continue(AddressSpace *as, hwaddr addr,
>              }
>          } else {
>              /* RAM case */
> -            ptr = qemu_ram_ptr_length(mr->ram_block, addr1, &l);
> +            ptr = qemu_ram_ptr_length(mr->ram_block, addr1, &l, false);
>              memcpy(buf, ptr, l);
>          }
>  
> @@ -3349,7 +3349,7 @@ void *address_space_map(AddressSpace *as,
>  
>      memory_region_ref(mr);
>      *plen = address_space_extend_translation(as, addr, len, mr, xlat, l, is_write);
> -    ptr = qemu_ram_ptr_length(mr->ram_block, xlat, plen);
> +    ptr = qemu_ram_ptr_length(mr->ram_block, xlat, plen, true);
>      rcu_read_unlock();
>  
>      return ptr;
> 

Queued, thanks.

Paolo