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Message-ID: <87mufms1oe.fsf@mpe.ellerman.id.au>
Date: Tue, 03 Sep 2019 09:45:05 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Michal Suchánek <msuchanek@...e.de>
Cc: linuxppc-dev@...ts.ozlabs.org,
Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>,
David Hildenbrand <david@...hat.com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Paul Mackerras <paulus@...ba.org>,
Breno Leitao <leitao@...ian.org>,
Michael Neuling <mikey@...ling.org>,
Diana Craciun <diana.craciun@....com>,
Firoz Khan <firoz.khan@...aro.org>,
Hari Bathini <hbathini@...ux.ibm.com>,
Joel Stanley <joel@....id.au>, Arnd Bergmann <arnd@...db.de>,
Nicholas Piggin <npiggin@...il.com>,
Alexander Viro <viro@...iv.linux.org.uk>,
Thomas Gleixner <tglx@...utronix.de>,
Allison Randal <allison@...utok.net>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-kernel@...r.kernel.org,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Andrew Donnellan <andrew.donnellan@....ibm.com>,
linux-fsdevel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v7 3/6] powerpc/perf: consolidate read_user_stack_32
Michal Suchánek <msuchanek@...e.de> writes:
> On Mon, 02 Sep 2019 14:01:17 +1000
> Michael Ellerman <mpe@...erman.id.au> wrote:
>> Michael Ellerman <mpe@...erman.id.au> writes:
>> > Michal Suchanek <msuchanek@...e.de> writes:
>> ...
>> >> @@ -295,6 +279,12 @@ static inline int current_is_64bit(void)
>> >> }
>> >>
>> >> #else /* CONFIG_PPC64 */
>> >> +static int read_user_stack_slow(void __user *ptr, void *buf, int nb)
>> >> +{
>> >> + return 0;
>> >> +}
>> >> +#endif /* CONFIG_PPC64 */
>> >
>> > Ending the PPC64 else case here, and then restarting it below with an
>> > ifndef means we end up with two parts of the file that define 32-bit
>> > code, with a common chunk in the middle, which I dislike.
>> >
>> > I'd rather you add the empty read_user_stack_slow() in the existing
>> > #else section and then move read_user_stack_32() below the whole ifdef
>> > PPC64/else/endif section.
>> >
>> > Is there some reason that doesn't work?
>>
>> Gah, I missed that you split the whole file later in the series. Any
>> reason you did it in two steps rather than moving patch 6 earlier in the
>> series?
>
> To make this patch readable.
But it's not very readable :)
You also retained the comment about the 32-bit behaviour which is now a
bit confusing, because the function is used on both 32 & 64-bit.
I think moving it as I suggested in my first reply makes for a better
diff, something like eg:
diff --git a/arch/powerpc/perf/callchain.c b/arch/powerpc/perf/callchain.c
index c84bbd4298a0..82c0f81b89a5 100644
--- a/arch/powerpc/perf/callchain.c
+++ b/arch/powerpc/perf/callchain.c
@@ -165,22 +165,6 @@ static int read_user_stack_64(unsigned long __user *ptr, unsigned long *ret)
return read_user_stack_slow(ptr, ret, 8);
}
-static int read_user_stack_32(unsigned int __user *ptr, unsigned int *ret)
-{
- if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned int) ||
- ((unsigned long)ptr & 3))
- return -EFAULT;
-
- pagefault_disable();
- if (!__get_user_inatomic(*ret, ptr)) {
- pagefault_enable();
- return 0;
- }
- pagefault_enable();
-
- return read_user_stack_slow(ptr, ret, 4);
-}
-
static inline int valid_user_sp(unsigned long sp, int is_64)
{
if (!sp || (sp & 7) || sp > (is_64 ? TASK_SIZE : 0x100000000UL) - 32)
@@ -295,27 +279,6 @@ static inline int current_is_64bit(void)
}
#else /* CONFIG_PPC64 */
-/*
- * On 32-bit we just access the address and let hash_page create a
- * HPTE if necessary, so there is no need to fall back to reading
- * the page tables. Since this is called at interrupt level,
- * do_page_fault() won't treat a DSI as a page fault.
- */
-static int read_user_stack_32(unsigned int __user *ptr, unsigned int *ret)
-{
- int rc;
-
- if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned int) ||
- ((unsigned long)ptr & 3))
- return -EFAULT;
-
- pagefault_disable();
- rc = __get_user_inatomic(*ret, ptr);
- pagefault_enable();
-
- return rc;
-}
-
static inline void perf_callchain_user_64(struct perf_callchain_entry_ctx *entry,
struct pt_regs *regs)
{
@@ -333,6 +296,11 @@ static inline int valid_user_sp(unsigned long sp, int is_64)
return 1;
}
+static int read_user_stack_slow(void __user *ptr, void *buf, int nb)
+{
+ return 0;
+}
+
#define __SIGNAL_FRAMESIZE32 __SIGNAL_FRAMESIZE
#define sigcontext32 sigcontext
#define mcontext32 mcontext
@@ -341,6 +309,33 @@ static inline int valid_user_sp(unsigned long sp, int is_64)
#endif /* CONFIG_PPC64 */
+static int read_user_stack_32(unsigned int __user *ptr, unsigned int *ret)
+{
+ int rc;
+
+ if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned int) ||
+ ((unsigned long)ptr & 3))
+ return -EFAULT;
+
+ pagefault_disable();
+ rc = __get_user_inatomic(*ret, ptr);
+ pagefault_enable();
+
+ /*
+ * On 32-bit we just access the address and let hash_page() create a
+ * HPTE if necessary, so there is no need to fall back to reading the
+ * page tables. Since this is called at interrupt level, do_page_fault()
+ * won't treat a DSI as a page fault.
+ *
+ * On 64-bit if the access faults we fall back to
+ * read_user_stack_slow(), see the comment there for more details.
+ */
+ if (IS_ENABLED(CONFIG_PPC64) && rc)
+ return read_user_stack_slow(ptr, ret, 4);
+
+ return rc;
+}
+
/*
* Layout for non-RT signal frames
*/
cheers
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