Re: [PATCHv4 07/10] kexec: Switch to __pa_symbol

Dave Young [off-list ref] writes:

Hi, Laura
On 11/29/16 at 10:55am, Laura Abbott wrote:

quoted

__pa_symbol is the correct api to get the physical address of kernel
symbols. Switch to it to allow for better debug checking.

I assume __pa_symbol is faster than __pa, but it still need some testing
on all arches which support kexec.

But seems long long ago there is a commit e3ebadd95cb in the commit log
I see below from:
"we should deprecate __pa_symbol(), and preferably __pa() too - and
 just use "virt_to_phys()" instead, which is is more readable and has
 nicer semantics."

But maybe in modern code __pa_symbol is prefered I may miss background.
virt_to_phys still sounds more readable now for me though.

There has been a lot of history with the various definitions.
__pa_symbol used to be x86 specific.

Now what we have is that __pa_symbol is just __pa(RELOC_HIDE(x));

Now arguably that whole reloc hide thing should happen by architectures
having a non-inline version of __pa as was done in the commit you
mention.  But at this point there appears to be nothing wrong with
changing a __pa to a __pa_symbol it might make things a tad more
reliable depending on the implementation of __pa.

Acked-by: "Eric W. Biederman" <redacted>


Eric

quoted

Signed-off-by: Laura Abbott <redacted>
---
Found during review of the kernel. Untested.
---
 kernel/kexec_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index 5616755..e1b625e 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c

@@ -1397,7 +1397,7 @@ void __weak arch_crash_save_vmcoreinfo(void)
 
 phys_addr_t __weak paddr_vmcoreinfo_note(void)
 {
-	return __pa((unsigned long)(char *)&vmcoreinfo_note);
+	return __pa_symbol((unsigned long)(char *)&vmcoreinfo_note);
 }
 
 static int __init crash_save_vmcoreinfo_init(void)

-- 
2.7.4


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http://lists.infradead.org/mailman/listinfo/kexec

Thanks
Dave

On 11/30/16 at 09:13pm, Eric W. Biederman wrote:

Dave Young [off-list ref] writes:

quoted

Hi, Laura
On 11/29/16 at 10:55am, Laura Abbott wrote:

quoted

__pa_symbol is the correct api to get the physical address of kernel
symbols. Switch to it to allow for better debug checking.

I assume __pa_symbol is faster than __pa, but it still need some testing
on all arches which support kexec.

But seems long long ago there is a commit e3ebadd95cb in the commit log
I see below from:
"we should deprecate __pa_symbol(), and preferably __pa() too - and
 just use "virt_to_phys()" instead, which is is more readable and has
 nicer semantics."

But maybe in modern code __pa_symbol is prefered I may miss background.
virt_to_phys still sounds more readable now for me though.

There has been a lot of history with the various definitions.
__pa_symbol used to be x86 specific.

Now what we have is that __pa_symbol is just __pa(RELOC_HIDE(x));

Now arguably that whole reloc hide thing should happen by architectures
having a non-inline version of __pa as was done in the commit you
mention.  But at this point there appears to be nothing wrong with
changing a __pa to a __pa_symbol it might make things a tad more
reliable depending on the implementation of __pa.

Then it is safe and reasonable, thanks for the clarification. 

Acked-by: "Eric W. Biederman" <redacted>


Eric

quoted

quoted

Signed-off-by: Laura Abbott <redacted>
---
Found during review of the kernel. Untested.
---
 kernel/kexec_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index 5616755..e1b625e 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c

@@ -1397,7 +1397,7 @@ void __weak arch_crash_save_vmcoreinfo(void)
 
 phys_addr_t __weak paddr_vmcoreinfo_note(void)
 {
-	return __pa((unsigned long)(char *)&vmcoreinfo_note);
+	return __pa_symbol((unsigned long)(char *)&vmcoreinfo_note);
 }
 
 static int __init crash_save_vmcoreinfo_init(void)

-- 
2.7.4


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Thanks
Dave