tcg: tb_lock removal redux v1

[Qemu-devel] [PATCH 08/16] translate-all: work page-by-page in tb_invalidate_phys_range_1

Posted by Emilio G. Cota 7 years, 7 months ago

So that we pass a same-page range to tb_invalidate_phys_page_range,
instead of always passing an end address that could be on a different
page.

As discussed with Peter Maydell on the list [1], tb_invalidate_phys_page_range
doesn't actually do much with 'end', which explains why we have never
hit a bug despite going against what the comment on top of
tb_invalidate_phys_page_range requires:

> * Invalidate all TBs which intersect with the target physical address range
> * [start;end[. NOTE: start and end must refer to the *same* physical page.

The appended honours the comment, which avoids confusion.

While at it, rework the loop into a for loop, which is less error prone
(e.g. "continue" won't result in an infinite loop).

[1] https://lists.gnu.org/archive/html/qemu-devel/2017-07/msg09165.html

Signed-off-by: Emilio G. Cota <cota@braap.org>
---
 accel/tcg/translate-all.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
index 816419a..a98e182 100644
--- a/accel/tcg/translate-all.c
+++ b/accel/tcg/translate-all.c
@@ -1381,10 +1381,14 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
  */
 static void tb_invalidate_phys_range_1(tb_page_addr_t start, tb_page_addr_t end)
 {
-    while (start < end) {
-        tb_invalidate_phys_page_range(start, end, 0);
-        start &= TARGET_PAGE_MASK;
-        start += TARGET_PAGE_SIZE;
+    tb_page_addr_t next;
+
+    for (next = (start & TARGET_PAGE_MASK) + TARGET_PAGE_SIZE;
+         start < end;
+         start = next, next += TARGET_PAGE_SIZE) {
+        tb_page_addr_t bound = MIN(next, end);
+
+        tb_invalidate_phys_page_range(start, bound, 0);
     }
 }
 
-- 
2.7.4

Re: [Qemu-devel] [PATCH 08/16] translate-all: work page-by-page in tb_invalidate_phys_range_1

Posted by Richard Henderson 7 years, 7 months ago

On 02/26/2018 09:39 PM, Emilio G. Cota wrote:
> So that we pass a same-page range to tb_invalidate_phys_page_range,
> instead of always passing an end address that could be on a different
> page.
> 
> As discussed with Peter Maydell on the list [1], tb_invalidate_phys_page_range
> doesn't actually do much with 'end', which explains why we have never
> hit a bug despite going against what the comment on top of
> tb_invalidate_phys_page_range requires:
> 
>> * Invalidate all TBs which intersect with the target physical address range
>> * [start;end[. NOTE: start and end must refer to the *same* physical page.
> The appended honours the comment, which avoids confusion.
> 
> While at it, rework the loop into a for loop, which is less error prone
> (e.g. "continue" won't result in an infinite loop).
> 
> [1] https://lists.gnu.org/archive/html/qemu-devel/2017-07/msg09165.html
> 
> Signed-off-by: Emilio G. Cota <cota@braap.org>
> ---

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~

Re: [Qemu-devel] [PATCH 08/16] translate-all: work page-by-page in tb_invalidate_phys_range_1

Posted by Alex Bennée 7 years, 6 months ago

Emilio G. Cota <cota@braap.org> writes:

> So that we pass a same-page range to tb_invalidate_phys_page_range,
> instead of always passing an end address that could be on a different
> page.
>
> As discussed with Peter Maydell on the list [1], tb_invalidate_phys_page_range
> doesn't actually do much with 'end', which explains why we have never
> hit a bug despite going against what the comment on top of
> tb_invalidate_phys_page_range requires:
>
>> * Invalidate all TBs which intersect with the target physical address range
>> * [start;end[. NOTE: start and end must refer to the *same* physical page.
>
> The appended honours the comment, which avoids confusion.
>
> While at it, rework the loop into a for loop, which is less error prone
> (e.g. "continue" won't result in an infinite loop).
>
> [1] https://lists.gnu.org/archive/html/qemu-devel/2017-07/msg09165.html
>
> Signed-off-by: Emilio G. Cota <cota@braap.org>

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

> ---
>  accel/tcg/translate-all.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
> index 816419a..a98e182 100644
> --- a/accel/tcg/translate-all.c
> +++ b/accel/tcg/translate-all.c
> @@ -1381,10 +1381,14 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
>   */
>  static void tb_invalidate_phys_range_1(tb_page_addr_t start, tb_page_addr_t end)
>  {
> -    while (start < end) {
> -        tb_invalidate_phys_page_range(start, end, 0);
> -        start &= TARGET_PAGE_MASK;
> -        start += TARGET_PAGE_SIZE;
> +    tb_page_addr_t next;
> +
> +    for (next = (start & TARGET_PAGE_MASK) + TARGET_PAGE_SIZE;
> +         start < end;
> +         start = next, next += TARGET_PAGE_SIZE) {
> +        tb_page_addr_t bound = MIN(next, end);
> +
> +        tb_invalidate_phys_page_range(start, bound, 0);
>      }
>  }


--
Alex Bennée

Re: [Qemu-devel] [PATCH 08/16] translate-all: work page-by-page in tb_invalidate_phys_range_1

Posted by Alex Bennée 7 years, 6 months ago

Emilio G. Cota <cota@braap.org> writes:

> So that we pass a same-page range to tb_invalidate_phys_page_range,
> instead of always passing an end address that could be on a different
> page.
>
> As discussed with Peter Maydell on the list [1], tb_invalidate_phys_page_range
> doesn't actually do much with 'end', which explains why we have never
> hit a bug despite going against what the comment on top of
> tb_invalidate_phys_page_range requires:
>
>> * Invalidate all TBs which intersect with the target physical address range
>> * [start;end[. NOTE: start and end must refer to the *same* physical page.
>
> The appended honours the comment, which avoids confusion.
>
> While at it, rework the loop into a for loop, which is less error prone
> (e.g. "continue" won't result in an infinite loop).
>
> [1] https://lists.gnu.org/archive/html/qemu-devel/2017-07/msg09165.html
>
> Signed-off-by: Emilio G. Cota <cota@braap.org>

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

> ---
>  accel/tcg/translate-all.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
> index 816419a..a98e182 100644
> --- a/accel/tcg/translate-all.c
> +++ b/accel/tcg/translate-all.c
> @@ -1381,10 +1381,14 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
>   */
>  static void tb_invalidate_phys_range_1(tb_page_addr_t start, tb_page_addr_t end)
>  {
> -    while (start < end) {
> -        tb_invalidate_phys_page_range(start, end, 0);
> -        start &= TARGET_PAGE_MASK;
> -        start += TARGET_PAGE_SIZE;
> +    tb_page_addr_t next;
> +
> +    for (next = (start & TARGET_PAGE_MASK) + TARGET_PAGE_SIZE;
> +         start < end;
> +         start = next, next += TARGET_PAGE_SIZE) {
> +        tb_page_addr_t bound = MIN(next, end);
> +
> +        tb_invalidate_phys_page_range(start, bound, 0);
>      }
>  }


--
Alex Bennée