From: Balbir Singh <bsingharora@gmail.com>
I ran into this issue while debugging an early boot problem.
The system hit a BUG_ON() but report bug failed to print the
line number and file name. The reason being that the system
was running in real mode and report_bug() searches for
addresses in the PAGE_OFFSET+ region
Suggested-by: Paul Mackerras <redacted>
Signed-off-by: Balbir Singh <bsingharora@gmail.com>
---
arch/powerpc/kernel/traps.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
goto bail;
}
if (reason & REASON_TRAP) {
+ unsigned long bugaddr;
/* Debugger is first in line to stop recursive faults in
* rcu_lock, notify_die, or atomic_notifier_call_chain */
if (debugger_bpt(regs))
From: Paul Mackerras <hidden> Date: 2016-02-17 04:56:09
On Wed, Feb 17, 2016 at 03:43:11PM +1100, Balbir Singh wrote:
quoted hunk
From: Balbir Singh <bsingharora@gmail.com>
I ran into this issue while debugging an early boot problem.
The system hit a BUG_ON() but report bug failed to print the
line number and file name. The reason being that the system
was running in real mode and report_bug() searches for
addresses in the PAGE_OFFSET+ region
Suggested-by: Paul Mackerras <redacted>
Signed-off-by: Balbir Singh <bsingharora@gmail.com>
---
arch/powerpc/kernel/traps.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
goto bail;
}
if (reason & REASON_TRAP) {
+ unsigned long bugaddr;
/* Debugger is first in line to stop recursive faults in
* rcu_lock, notify_die, or atomic_notifier_call_chain */
if (debugger_bpt(regs))
It might be a little better to do this:
bugaddr = regs->nip;
if (REGION_ID(bugaddr) == 0 && !(regs->msr & MSR_IR))
bugaddr += PAGE_OFFSET;
It is possible to execute from addresses with the 0xc000... on top in
real mode, because the CPU ignores the top 4 address bits in real
mode.
Paul.
It might be a little better to do this:
bugaddr = regs->nip;
if (REGION_ID(bugaddr) == 0 && !(regs->msr & MSR_IR))
bugaddr += PAGE_OFFSET;
It is possible to execute from addresses with the 0xc000... on top in
real mode, because the CPU ignores the top 4 address bits in real
mode.
Good catch! Thank you
Changelog:
Don't add PAGE_OFFSET blindly, check if REGION_ID is 0
I ran into this issue while debugging an early boot problem.
The system hit a BUG_ON() but report bug failed to print the
line number and file name. The reason being that the system
was running in real mode and report_bug() searches for
addresses in the PAGE_OFFSET+ region
Suggested-by: Paul Mackerras <redacted>
Signed-off-by: Balbir Singh <bsingharora@gmail.com>
---
arch/powerpc/kernel/traps.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
goto bail;
}
if (reason & REASON_TRAP) {
+ unsigned long bugaddr;
/* Debugger is first in line to stop recursive faults in
* rcu_lock, notify_die, or atomic_notifier_call_chain */
if (debugger_bpt(regs))
From: Paul Mackerras <hidden> Date: 2016-02-17 08:23:50
On Wed, Feb 17, 2016 at 01:33:32PM +0530, Anshuman Khandual wrote:
On 02/17/2016 12:46 PM, Balbir Singh wrote:
quoted
quoted
quoted
It might be a little better to do this:
bugaddr = regs->nip;
if (REGION_ID(bugaddr) == 0 && !(regs->msr & MSR_IR))
bugaddr += PAGE_OFFSET;
It is possible to execute from addresses with the 0xc000... on top in
real mode, because the CPU ignores the top 4 address bits in real
mode.
Good catch! Thank you
Changelog:
Don't add PAGE_OFFSET blindly, check if REGION_ID is 0
Cant we use USER_REGION_ID directly ?
If we use USER_REGION_ID then the reader needs to know that the user
region is region 0 to understand the code. Thus I think it is clearer
to use REGION_ID(bugaddr) == 0. Whether or not the address is a user
region address is not really relevant to the question of whether it's
a physical address being accessed directly in real mode vs. a kernel
virtual address, which is what we're trying to determine.
Paul.
It might be a little better to do this:
bugaddr = regs->nip;
if (REGION_ID(bugaddr) == 0 && !(regs->msr & MSR_IR))
bugaddr += PAGE_OFFSET;
It is possible to execute from addresses with the 0xc000... on top in
real mode, because the CPU ignores the top 4 address bits in real
mode.
Good catch! Thank you
Changelog:
Don't add PAGE_OFFSET blindly, check if REGION_ID is 0
It might be a little better to do this:
=20
bugaddr =3D regs->nip;
if (REGION_ID(bugaddr) =3D=3D 0 && !(regs->msr & MSR_IR))
bugaddr +=3D PAGE_OFFSET;
=20
It is possible to execute from addresses with the 0xc000... on top in
real mode, because the CPU ignores the top 4 address bits in real
mode.
Good catch! Thank you
Changelog:
Don't add PAGE_OFFSET blindly, check if REGION_ID is 0
I ran into this issue while debugging an early boot problem.
The system hit a BUG_ON() but report bug failed to print the
line number and file name. The reason being that the system
was running in real mode and report_bug() searches for
addresses in the PAGE_OFFSET+ region
Suggested-by: Paul Mackerras <redacted>
Signed-off-by: Balbir Singh <bsingharora@gmail.com>
---
=C2=A0arch/powerpc/kernel/traps.c | 7 ++++++-
=C2=A01 file changed, 6 insertions(+), 1 deletion(-)
=C2=A0 goto bail;
=C2=A0 }
=C2=A0 if (reason & REASON_TRAP) {
+ unsigned long bugaddr;
=C2=A0 /* Debugger is first in line to stop recursive faults in
=C2=A0 =C2=A0* rcu_lock, notify_die, or atomic_notifier_call_chain */
=C2=A0 if (debugger_bpt(regs))
Can we add some comments around this. When i looked at this first, i was
wondering how nip can be in user region. But then realized that what we
are checking here is kernel address used in real mode. The use of
REGION_ID eventhough simpler is confusing. Hence adding the comment with
details Paul mentioned in email will help.
=C2=A0 if (!(regs->msr & MSR_PR) &&=C2=A0=C2=A0/* not user-mode */
- =C2=A0=C2=A0=C2=A0=C2=A0report_bug(regs->nip, regs) =3D=3D BUG_TRAP_TY=
Changelog:
Don't add PAGE_OFFSET blindly, check if REGION_ID is 0
I ran into this issue while debugging an early boot problem.
The system hit a BUG_ON() but report bug failed to print the
line number and file name. The reason being that the system
was running in real mode and report_bug() searches for
addresses in the PAGE_OFFSET+ region
Suggested-by: Paul Mackerras <redacted>
Signed-off-by: Balbir Singh <bsingharora@gmail.com>
<snip>
Can we add some comments around this. When i looked at this first, i was
wondering how nip can be in user region. But then realized that what we
are checking here is kernel address used in real mode. The use of
REGION_ID eventhough simpler is confusing. Hence adding the comment with
details Paul mentioned in email will help.
I've tried and covered it in the changelog, I thought a code comment
would make sense for the very non obvious cases and not repeat what
the code does as comment
Balbir Singh.
Changelog:
Don't add PAGE_OFFSET blindly, check if REGION_ID is 0
I ran into this issue while debugging an early boot problem.
The system hit a BUG_ON() but report bug failed to print the
line number and file name. The reason being that the system
was running in real mode and report_bug() searches for
addresses in the PAGE_OFFSET+ region
Suggested-by: Paul Mackerras <redacted>
Signed-off-by: Balbir Singh <bsingharora@gmail.com>
<snip>
quoted
Can we add some comments around this. When i looked at this first, i was
wondering how nip can be in user region. But then realized that what we
are checking here is kernel address used in real mode. The use of
REGION_ID eventhough simpler is confusing. Hence adding the comment with
details Paul mentioned in email will help.
I've tried and covered it in the changelog, I thought a code comment
would make sense for the very non obvious cases and not repeat what
the code does as comment
The use of REGION_ID indicate that you are checking for region. Hence
the suggestion. Looking at this again, I suggest we should add a new
macro or will have to open code it. Because in the radix series we make
REGION_ID a hash config thing and this is generic stuff.
-aneesh