[PATCH] arm64: cacheflush: Fix KGDB trap detection

[PATCH] arm64: cacheflush: Fix KGDB trap detection

[Daniel Thompson]

flush_icache_range() contains a bodge to avoid issuing IPIs when the kgdb
trap handler is running because issuing IPIs is unsafe (and unnecessary)
in this exection context. However the current test is flawed: it both
over-matches (could skip the IPI when the kgdb trap is not running) and
under-matches (does not skip the IPI for all kgdb cache operations).

Fix by replacing the ad-hoc check with the proper kgdb macro. This also
allows us to drop the #ifdef wrapper.

Fixes: 3b8c9f1cdfc5 ("arm64: IPI each CPU after invalidating the I-cache for kernel mappings")
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
---
 arch/arm64/include/asm/cacheflush.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/cacheflush.h b/arch/arm64/include/asm/cacheflush.h
index e6cca3d4acf7..ce50c1f1f1ea 100644
--- a/arch/arm64/include/asm/cacheflush.h
+++ b/arch/arm64/include/asm/cacheflush.h
@@ -79,7 +79,7 @@ static inline void flush_icache_range(unsigned long start, unsigned long end)
 	 * IPI all online CPUs so that they undergo a context synchronization
 	 * event and are forced to refetch the new instructions.
 	 */
-#ifdef CONFIG_KGDB
+
 	/*
 	 * KGDB performs cache maintenance with interrupts disabled, so we
 	 * will deadlock trying to IPI the secondary CPUs. In theory, we can
@@ -89,9 +89,9 @@ static inline void flush_icache_range(unsigned long start, unsigned long end)
 	 * the patching operation, so we don't need extra IPIs here anyway.
 	 * In which case, add a KGDB-specific bodge and return early.
 	 */
-	if (kgdb_connected && irqs_disabled())
+	if (in_dbg_master())
 		return;
-#endif
+
 	kick_all_cpus_sync();
 }


base-commit: 6a8b55ed4056ea5559ebe4f6a4b247f627870d4c
--
2.25.1

Re: [PATCH] arm64: cacheflush: Fix KGDB trap detection

[Doug Anderson]

Hi,

On Fri, May 1, 2020 at 9:20 AM Daniel Thompson
<daniel.thompson@linaro.org> wrote:
>
> flush_icache_range() contains a bodge to avoid issuing IPIs when the kgdb
> trap handler is running because issuing IPIs is unsafe (and unnecessary)
> in this exection context. However the current test is flawed: it both

s/exection/execution/

> over-matches (could skip the IPI when the kgdb trap is not running) and
> under-matches (does not skip the IPI for all kgdb cache operations).

Maybe explain why?  I believe this is because "kgdb_connected"
signifies that a host "gdb" is connected.

* If we're sitting at the kdb prompt "kgdb_connected" won't be set but
we might still try to do something with a breakpoint with interrupts
off.

* If we are currently _not_ stopped in the debugger but the host "gdb"
is connected then "kgdb_connected" will continue to be set.  In this
context we will exit early if any other callers happen to try to cache
flush with interrupts disabled.


> Fix by replacing the ad-hoc check with the proper kgdb macro. This also
> allows us to drop the #ifdef wrapper.
>
> Fixes: 3b8c9f1cdfc5 ("arm64: IPI each CPU after invalidating the I-cache for kernel mappings")
> Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
> ---
>  arch/arm64/include/asm/cacheflush.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)

Other than the suggestions to the commit message:

Reviewed-by: Douglas Anderson <dianders@chromium.org>