Replace read_atomic() with ACCESS_ONCE() to match the intended use, that
is, to prevent the compiler from (via optimization) reading shared
memory more than once.

Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
---
 xen/arch/arm/tee/ffa_shm.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/xen/arch/arm/tee/ffa_shm.c b/xen/arch/arm/tee/ffa_shm.c
index eed9ad2d2986..75a5b66aeb4c 100644
--- a/xen/arch/arm/tee/ffa_shm.c
+++ b/xen/arch/arm/tee/ffa_shm.c
@@ -7,6 +7,7 @@
 #include <xen/sizes.h>
 #include <xen/types.h>
 #include <xen/mm.h>
+#include <xen/lib.h>
 #include <xen/list.h>
 #include <xen/spinlock.h>
 
@@ -171,8 +172,8 @@ static int get_shm_pages(struct domain *d, struct ffa_shm_mem *shm,
 
     for ( n = 0; n < range_count; n++ )
     {
-        page_count = read_atomic(&range[n].page_count);
-        addr = read_atomic(&range[n].address);
+        page_count = ACCESS_ONCE(range[n].page_count);
+        addr = ACCESS_ONCE(range[n].address);
         for ( m = 0; m < page_count; m++ )
         {
             if ( pg_idx >= shm->page_count )
@@ -527,13 +528,13 @@ void ffa_handle_mem_share(struct cpu_user_regs *regs)
         goto out_unlock;
 
     mem_access = ctx->tx + trans.mem_access_offs;
-    if ( read_atomic(&mem_access->access_perm.perm) != FFA_MEM_ACC_RW )
+    if ( ACCESS_ONCE(mem_access->access_perm.perm) != FFA_MEM_ACC_RW )
     {
         ret = FFA_RET_NOT_SUPPORTED;
         goto out_unlock;
     }
 
-    region_offs = read_atomic(&mem_access->region_offs);
+    region_offs = ACCESS_ONCE(mem_access->region_offs);
     if ( sizeof(*region_descr) + region_offs > frag_len )
     {
         ret = FFA_RET_NOT_SUPPORTED;
@@ -541,8 +542,8 @@ void ffa_handle_mem_share(struct cpu_user_regs *regs)
     }
 
     region_descr = ctx->tx + region_offs;
-    range_count = read_atomic(&region_descr->address_range_count);
-    page_count = read_atomic(&region_descr->total_page_count);
+    range_count = ACCESS_ONCE(region_descr->address_range_count);
+    page_count = ACCESS_ONCE(region_descr->total_page_count);
 
     if ( !page_count )
     {
@@ -557,7 +558,7 @@ void ffa_handle_mem_share(struct cpu_user_regs *regs)
         goto out_unlock;
     }
     shm->sender_id = trans.sender_id;
-    shm->ep_id = read_atomic(&mem_access->access_perm.endpoint_id);
+    shm->ep_id = ACCESS_ONCE(mem_access->access_perm.endpoint_id);
 
     /*
      * Check that the Composite memory region descriptor fits.
-- 
2.34.1

Hi Jens,

> On 9 Apr 2024, at 17:36, Jens Wiklander <jens.wiklander@linaro.org> wrote:
> 
> Replace read_atomic() with ACCESS_ONCE() to match the intended use, that
> is, to prevent the compiler from (via optimization) reading shared
> memory more than once.

This definitely makes sense.

> 
> Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>

Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>

Cheers
Bertrand

> ---
> xen/arch/arm/tee/ffa_shm.c | 15 ++++++++-------
> 1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/xen/arch/arm/tee/ffa_shm.c b/xen/arch/arm/tee/ffa_shm.c
> index eed9ad2d2986..75a5b66aeb4c 100644
> --- a/xen/arch/arm/tee/ffa_shm.c
> +++ b/xen/arch/arm/tee/ffa_shm.c
> @@ -7,6 +7,7 @@
> #include <xen/sizes.h>
> #include <xen/types.h>
> #include <xen/mm.h>
> +#include <xen/lib.h>
> #include <xen/list.h>
> #include <xen/spinlock.h>
> 
> @@ -171,8 +172,8 @@ static int get_shm_pages(struct domain *d, struct ffa_shm_mem *shm,
> 
>     for ( n = 0; n < range_count; n++ )
>     {
> -        page_count = read_atomic(&range[n].page_count);
> -        addr = read_atomic(&range[n].address);
> +        page_count = ACCESS_ONCE(range[n].page_count);
> +        addr = ACCESS_ONCE(range[n].address);
>         for ( m = 0; m < page_count; m++ )
>         {
>             if ( pg_idx >= shm->page_count )
> @@ -527,13 +528,13 @@ void ffa_handle_mem_share(struct cpu_user_regs *regs)
>         goto out_unlock;
> 
>     mem_access = ctx->tx + trans.mem_access_offs;
> -    if ( read_atomic(&mem_access->access_perm.perm) != FFA_MEM_ACC_RW )
> +    if ( ACCESS_ONCE(mem_access->access_perm.perm) != FFA_MEM_ACC_RW )
>     {
>         ret = FFA_RET_NOT_SUPPORTED;
>         goto out_unlock;
>     }
> 
> -    region_offs = read_atomic(&mem_access->region_offs);
> +    region_offs = ACCESS_ONCE(mem_access->region_offs);
>     if ( sizeof(*region_descr) + region_offs > frag_len )
>     {
>         ret = FFA_RET_NOT_SUPPORTED;
> @@ -541,8 +542,8 @@ void ffa_handle_mem_share(struct cpu_user_regs *regs)
>     }
> 
>     region_descr = ctx->tx + region_offs;
> -    range_count = read_atomic(&region_descr->address_range_count);
> -    page_count = read_atomic(&region_descr->total_page_count);
> +    range_count = ACCESS_ONCE(region_descr->address_range_count);
> +    page_count = ACCESS_ONCE(region_descr->total_page_count);
> 
>     if ( !page_count )
>     {
> @@ -557,7 +558,7 @@ void ffa_handle_mem_share(struct cpu_user_regs *regs)
>         goto out_unlock;
>     }
>     shm->sender_id = trans.sender_id;
> -    shm->ep_id = read_atomic(&mem_access->access_perm.endpoint_id);
> +    shm->ep_id = ACCESS_ONCE(mem_access->access_perm.endpoint_id);
> 
>     /*
>      * Check that the Composite memory region descriptor fits.
> -- 
> 2.34.1
>