[PATCH v3] hw/i386/intel_iommu: Simplify vtd_find_as_from_bus_num() logic

[PATCH v3] hw/i386/intel_iommu: Simplify vtd_find_as_from_bus_num() logic

[Philippe Mathieu-Daudé]

The vtd_find_as_from_bus_num() function was introduced (in commit
dbaabb25f) in a code format that could return an incorrect pointer,
which was later fixed by commit a2e1cd41ccf.
We could have avoid this by writing the if() statement differently.
Do it now, in case this function is re-used. The code is easier to
review (harder to miss bugs).

Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
Since v2: Re-worded commit description, patch sent without -w.
Since v3: patch send without diff

This patch is easier to review with 'git-diff -w' (--ignore-all-space)
---
 hw/i386/intel_iommu.c | 34 ++++++++++++++++++----------------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index 6258c58ac9..e720a8939c 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -987,24 +987,26 @@ static bool vtd_slpte_nonzero_rsvd(uint64_t slpte, uint32_t level)
 static VTDBus *vtd_find_as_from_bus_num(IntelIOMMUState *s, uint8_t bus_num)
 {
     VTDBus *vtd_bus = s->vtd_as_by_bus_num[bus_num];
-    if (!vtd_bus) {
-        /*
-         * Iterate over the registered buses to find the one which
-         * currently hold this bus number, and update the bus_num
-         * lookup table:
-         */
-        GHashTableIter iter;
+    GHashTableIter iter;
 
-        g_hash_table_iter_init(&iter, s->vtd_as_by_busptr);
-        while (g_hash_table_iter_next(&iter, NULL, (void **)&vtd_bus)) {
-            if (pci_bus_num(vtd_bus->bus) == bus_num) {
-                s->vtd_as_by_bus_num[bus_num] = vtd_bus;
-                return vtd_bus;
-            }
-        }
-        vtd_bus = NULL;
+    if (vtd_bus) {
+        return vtd_bus;
     }
-    return vtd_bus;
+
+    /*
+     * Iterate over the registered buses to find the one which
+     * currently hold this bus number, and update the bus_num
+     * lookup table:
+     */
+    g_hash_table_iter_init(&iter, s->vtd_as_by_busptr);
+    while (g_hash_table_iter_next(&iter, NULL, (void **)&vtd_bus)) {
+        if (pci_bus_num(vtd_bus->bus) == bus_num) {
+            s->vtd_as_by_bus_num[bus_num] = vtd_bus;
+            return vtd_bus;
+        }
+    }
+
+    return NULL;
 }
 
 /* Given the @iova, get relevant @slptep. @slpte_level will be the last level
-- 
2.21.1

Re: [PATCH v3] hw/i386/intel_iommu: Simplify vtd_find_as_from_bus_num() logic

[Auger Eric]

Hi Philippe,

On 2/27/20 8:46 AM, Philippe Mathieu-Daudé wrote:
> The vtd_find_as_from_bus_num() function was introduced (in commit
> dbaabb25f) in a code format that could return an incorrect pointer,
> which was later fixed by commit a2e1cd41ccf.
> We could have avoid this by writing the if() statement differently.
s/avoid/avoided
> Do it now, in case this function is re-used. The code is easier to
> review (harder to miss bugs).
> 
> Reviewed-by: Peter Xu <peterx@redhat.com>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
> Since v2: Re-worded commit description, patch sent without -w.
> Since v3: patch send without diff
> 
> This patch is easier to review with 'git-diff -w' (--ignore-all-space)
> ---
>  hw/i386/intel_iommu.c | 34 ++++++++++++++++++----------------
>  1 file changed, 18 insertions(+), 16 deletions(-)
> 
> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> index 6258c58ac9..e720a8939c 100644
> --- a/hw/i386/intel_iommu.c
> +++ b/hw/i386/intel_iommu.c
> @@ -987,24 +987,26 @@ static bool vtd_slpte_nonzero_rsvd(uint64_t slpte, uint32_t level)
>  static VTDBus *vtd_find_as_from_bus_num(IntelIOMMUState *s, uint8_t bus_num)
>  {
>      VTDBus *vtd_bus = s->vtd_as_by_bus_num[bus_num];
> -    if (!vtd_bus) {
> -        /*
> -         * Iterate over the registered buses to find the one which
> -         * currently hold this bus number, and update the bus_num
s/hold/holds
> -         * lookup table:
I would change the comment that way

Iterate over the registered buses to find the one which
currently holds this bus number and update the bus_num
lookup table

> -         */
> -        GHashTableIter iter;
> +    GHashTableIter iter;
>  
> -        g_hash_table_iter_init(&iter, s->vtd_as_by_busptr);
> -        while (g_hash_table_iter_next(&iter, NULL, (void **)&vtd_bus)) {
> -            if (pci_bus_num(vtd_bus->bus) == bus_num) {
> -                s->vtd_as_by_bus_num[bus_num] = vtd_bus;
> -                return vtd_bus;
> -            }
> -        }
> -        vtd_bus = NULL;
> +    if (vtd_bus) {
> +        return vtd_bus;
>      }
> -    return vtd_bus;
> +
> +    /*
> +     * Iterate over the registered buses to find the one which
> +     * currently hold this bus number, and update the bus_num
> +     * lookup table:
> +     */
> +    g_hash_table_iter_init(&iter, s->vtd_as_by_busptr);
> +    while (g_hash_table_iter_next(&iter, NULL, (void **)&vtd_bus)) {
> +        if (pci_bus_num(vtd_bus->bus) == bus_num) {
> +            s->vtd_as_by_bus_num[bus_num] = vtd_bus;
> +            return vtd_bus;
> +        }
> +    }
> +
> +    return NULL;
>  }
>  
>  /* Given the @iova, get relevant @slptep. @slpte_level will be the last level
> 

Besides

Reviewed-by: Eric Auger <eric.auger@redhat.com>

Thanks

Eric