* [PATCH 0/2] Disable ftrace during kvm guest entry/exit
@ 2018-03-19 9:12 Naveen N. Rao
2018-03-19 9:13 ` [PATCH 1/2] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths Naveen N. Rao
2018-03-19 9:13 ` [PATCH 2/2] powerpc64/ftrace: Disable ftrace during kvm guest entry/exit Naveen N. Rao
0 siblings, 2 replies; 10+ messages in thread
From: Naveen N. Rao @ 2018-03-19 9:12 UTC (permalink / raw)
To: Steven Rostedt, Michael Ellerman, Paul Mackerras
Cc: linuxppc-dev, Benjamin Herrenschmidt, Anton Blanchard,
Nicholas Piggin, sathnaga
This is a follow on from the RFC posted at:
https://www.mail-archive.com/linuxppc-dev@lists.ozlabs.org/msg130047.html
This series implements a new field in paca called 'ftrace_disabled' to
be set whenever we want to skip function tracing. This is currently only
used by KVM guest entry/exit and as such, it is guarded in CONFIG_KVM as
suggested by Steven Rostedt. This has had some minimal testing, and I
will continue to test it this week and report back if I see any issues.
- Naveen
Naveen N. Rao (2):
powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code
paths
powerpc64/ftrace: Disable ftrace during kvm guest entry/exit
arch/powerpc/include/asm/paca.h | 1 +
arch/powerpc/kernel/asm-offsets.c | 1 +
arch/powerpc/kernel/trace/ftrace_64_mprofile.S | 13 +++++++++++++
arch/powerpc/kernel/trace/ftrace_64_pg.S | 6 ++++++
arch/powerpc/kvm/book3s_hv_rmhandlers.S | 8 ++++++++
5 files changed, 29 insertions(+)
--
2.16.2
^ permalink raw reply [flat|nested] 10+ messages in thread
* [PATCH 1/2] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths
2018-03-19 9:12 [PATCH 0/2] Disable ftrace during kvm guest entry/exit Naveen N. Rao
@ 2018-03-19 9:13 ` Naveen N. Rao
2018-03-19 10:40 ` Nicholas Piggin
2018-03-19 14:13 ` Steven Rostedt
2018-03-19 9:13 ` [PATCH 2/2] powerpc64/ftrace: Disable ftrace during kvm guest entry/exit Naveen N. Rao
1 sibling, 2 replies; 10+ messages in thread
From: Naveen N. Rao @ 2018-03-19 9:13 UTC (permalink / raw)
To: Steven Rostedt, Michael Ellerman, Paul Mackerras
Cc: linuxppc-dev, Benjamin Herrenschmidt, Anton Blanchard,
Nicholas Piggin, sathnaga
We have some C code that we call into from real mode where we cannot
take any exceptions. Though the C functions themselves are mostly safe,
if these functions are traced, there is a possibility that we may take
an exception. For instance, in certain conditions, the ftrace code uses
WARN(), which uses a 'trap' to do its job.
For such scenarios, introduce a new field in paca 'ftrace_disabled',
which is checked on ftrace entry before continuing. This field can then
be set to a non-zero value to disable/pause ftrace, and reset to zero to
resume ftrace.
Since KVM is the only user for this currently, we guard the
ftrace/mcount checks within CONFIG_KVM. This can later be removed
if/when there are other users.
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
arch/powerpc/include/asm/paca.h | 1 +
arch/powerpc/kernel/asm-offsets.c | 1 +
arch/powerpc/kernel/trace/ftrace_64_mprofile.S | 13 +++++++++++++
arch/powerpc/kernel/trace/ftrace_64_pg.S | 6 ++++++
4 files changed, 21 insertions(+)
diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
index d2bf71dddbef..4f47adc2a408 100644
--- a/arch/powerpc/include/asm/paca.h
+++ b/arch/powerpc/include/asm/paca.h
@@ -211,6 +211,7 @@ struct paca_struct {
u16 in_mce;
u8 hmi_event_available; /* HMI event is available */
u8 hmi_p9_special_emu; /* HMI P9 special emulation */
+ u8 ftrace_disabled;
#endif
/* Stuff for accurate time accounting */
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index ea5eb91b836e..8e4fc96ff6bc 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -240,6 +240,7 @@ int main(void)
OFFSET(PACA_RFI_FLUSH_FALLBACK_AREA, paca_struct, rfi_flush_fallback_area);
OFFSET(PACA_EXRFI, paca_struct, exrfi);
OFFSET(PACA_L1D_FLUSH_SIZE, paca_struct, l1d_flush_size);
+ OFFSET(PACA_FTRACE_DISABLED, paca_struct, ftrace_disabled);
#endif
OFFSET(PACAHWCPUID, paca_struct, hw_cpu_id);
diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
index 3f3e81852422..fdf702b4df25 100644
--- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
+++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
@@ -60,6 +60,19 @@ _GLOBAL(ftrace_caller)
mfxer r10
mfcr r11
+#ifdef CONFIG_KVM
+ lbz r3, PACA_FTRACE_DISABLED(r13)
+ cmpdi r3, 0
+ beq 1f
+ mflr r3
+ mtctr r3
+ REST_GPR(3, r1)
+ addi r1, r1, SWITCH_FRAME_SIZE
+ mtlr r0
+ bctr
+1:
+#endif
+
/* Get the _mcount() call site out of LR */
mflr r7
/* Save it as pt_regs->nip */
diff --git a/arch/powerpc/kernel/trace/ftrace_64_pg.S b/arch/powerpc/kernel/trace/ftrace_64_pg.S
index f095358da96e..5b2a99129322 100644
--- a/arch/powerpc/kernel/trace/ftrace_64_pg.S
+++ b/arch/powerpc/kernel/trace/ftrace_64_pg.S
@@ -16,6 +16,12 @@
#ifdef CONFIG_DYNAMIC_FTRACE
_GLOBAL_TOC(ftrace_caller)
+#ifdef CONFIG_KVM
+ lbz r3, PACA_FTRACE_DISABLED(r13)
+ cmpdi r3, 0
+ bnelr
+#endif
+
/* Taken from output of objdump from lib64/glibc */
mflr r3
ld r11, 0(r1)
--
2.16.2
^ permalink raw reply related [flat|nested] 10+ messages in thread
* [PATCH 2/2] powerpc64/ftrace: Disable ftrace during kvm guest entry/exit
2018-03-19 9:12 [PATCH 0/2] Disable ftrace during kvm guest entry/exit Naveen N. Rao
2018-03-19 9:13 ` [PATCH 1/2] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths Naveen N. Rao
@ 2018-03-19 9:13 ` Naveen N. Rao
1 sibling, 0 replies; 10+ messages in thread
From: Naveen N. Rao @ 2018-03-19 9:13 UTC (permalink / raw)
To: Steven Rostedt, Michael Ellerman, Paul Mackerras
Cc: linuxppc-dev, Benjamin Herrenschmidt, Anton Blanchard,
Nicholas Piggin, sathnaga
During guest entry/exit, we switch over to/from the guest MMU context.
While doing so, we set our state to KVM_GUEST_MODE_HOST_HV to note down
the fact that we cannot take any exceptions in the hypervisor code.
Since ftrace may be enabled and since it can result in us taking a trap,
disable ftrace by setting paca->ftrace_disabled. Once we exit the guest
and restore host MMU context, we re-enable ftrace.
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
arch/powerpc/kvm/book3s_hv_rmhandlers.S | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index f31f357b8c5a..9292087adb68 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -600,6 +600,10 @@ kvmppc_hv_entry:
/* Save R1 in the PACA */
std r1, HSTATE_HOST_R1(r13)
+ /* Disable ftrace since we can't take a trap any more */
+ li r6, 1
+ stb r6, PACA_FTRACE_DISABLED(r13)
+
li r6, KVM_GUEST_MODE_HOST_HV
stb r6, HSTATE_IN_GUEST(r13)
@@ -2048,6 +2052,8 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_TYPE_RADIX)
/* Unset guest mode */
li r0, KVM_GUEST_MODE_NONE
stb r0, HSTATE_IN_GUEST(r13)
+ li r0, 0
+ stb r0, PACA_FTRACE_DISABLED(r13)
ld r0, SFS+PPC_LR_STKOFF(r1)
addi r1, r1, SFS
@@ -3379,6 +3385,8 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_TYPE_RADIX)
ld r8, KVM_HOST_LPCR(r10)
mtspr SPRN_LPCR, r8
isync
+ li r0, 0
+ stb r0, PACA_FTRACE_DISABLED(r13)
li r0, KVM_GUEST_MODE_NONE
stb r0, HSTATE_IN_GUEST(r13)
--
2.16.2
^ permalink raw reply related [flat|nested] 10+ messages in thread
* Re: [PATCH 1/2] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths
2018-03-19 9:13 ` [PATCH 1/2] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths Naveen N. Rao
@ 2018-03-19 10:40 ` Nicholas Piggin
2018-03-19 18:53 ` Naveen N. Rao
2018-03-19 22:34 ` Michael Ellerman
2018-03-19 14:13 ` Steven Rostedt
1 sibling, 2 replies; 10+ messages in thread
From: Nicholas Piggin @ 2018-03-19 10:40 UTC (permalink / raw)
To: Naveen N. Rao
Cc: Steven Rostedt, Michael Ellerman, Paul Mackerras, linuxppc-dev,
Benjamin Herrenschmidt, Anton Blanchard, sathnaga
On Mon, 19 Mar 2018 14:43:00 +0530
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
> We have some C code that we call into from real mode where we cannot
> take any exceptions. Though the C functions themselves are mostly safe,
> if these functions are traced, there is a possibility that we may take
> an exception. For instance, in certain conditions, the ftrace code uses
> WARN(), which uses a 'trap' to do its job.
>
> For such scenarios, introduce a new field in paca 'ftrace_disabled',
> which is checked on ftrace entry before continuing. This field can then
> be set to a non-zero value to disable/pause ftrace, and reset to zero to
> resume ftrace.
>
> Since KVM is the only user for this currently, we guard the
> ftrace/mcount checks within CONFIG_KVM. This can later be removed
> if/when there are other users.
Why not test HSTATE_IN_GUEST then? Add ftrace_disabled if non-KVM users
come along.
Thanks,
Nick
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 1/2] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths
2018-03-19 9:13 ` [PATCH 1/2] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths Naveen N. Rao
2018-03-19 10:40 ` Nicholas Piggin
@ 2018-03-19 14:13 ` Steven Rostedt
2018-03-19 18:54 ` Naveen N. Rao
1 sibling, 1 reply; 10+ messages in thread
From: Steven Rostedt @ 2018-03-19 14:13 UTC (permalink / raw)
To: Naveen N. Rao
Cc: Michael Ellerman, Paul Mackerras, linuxppc-dev,
Benjamin Herrenschmidt, Anton Blanchard, Nicholas Piggin,
sathnaga
On Mon, 19 Mar 2018 14:43:00 +0530
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
> diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
> index 3f3e81852422..fdf702b4df25 100644
> --- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
> +++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
> @@ -60,6 +60,19 @@ _GLOBAL(ftrace_caller)
> mfxer r10
> mfcr r11
>
> +#ifdef CONFIG_KVM
> + lbz r3, PACA_FTRACE_DISABLED(r13)
> + cmpdi r3, 0
> + beq 1f
> + mflr r3
> + mtctr r3
> + REST_GPR(3, r1)
> + addi r1, r1, SWITCH_FRAME_SIZE
> + mtlr r0
> + bctr
> +1:
> +#endif
I wonder if we should try to move the return out of the fast path (for
cache reasons), as most of the time the above compare will be true. That
is:
#ifdef CONFIG_KVM
lbz r3, PACA_FTRACE_DISABLED(r13)
cmpdi r3, 0
bne no_trace
#endif
/* rest of ftrace_caller code */
/* after ftrace_caller... */
bctr /* jump after _mcount site */
#ifdef CONFIG_KVM
no_trace:
mflr r3
mtctr r3
REST_GPR(3, r1)
addi r1, r1, SWITCH_FRAME_SIZE
mtlr r0
bctr
#endif
-- Steve
> +
> /* Get the _mcount() call site out of LR */
> mflr r7
> /* Save it as pt_regs->nip */
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 1/2] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths
2018-03-19 10:40 ` Nicholas Piggin
@ 2018-03-19 18:53 ` Naveen N. Rao
2018-03-19 22:34 ` Michael Ellerman
1 sibling, 0 replies; 10+ messages in thread
From: Naveen N. Rao @ 2018-03-19 18:53 UTC (permalink / raw)
To: Nicholas Piggin
Cc: Anton Blanchard, Benjamin Herrenschmidt, linuxppc-dev,
Michael Ellerman, Paul Mackerras, Steven Rostedt, sathnaga
Nicholas Piggin wrote:
> On Mon, 19 Mar 2018 14:43:00 +0530
> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
>=20
>> We have some C code that we call into from real mode where we cannot
>> take any exceptions. Though the C functions themselves are mostly safe,
>> if these functions are traced, there is a possibility that we may take
>> an exception. For instance, in certain conditions, the ftrace code uses
>> WARN(), which uses a 'trap' to do its job.
>>=20
>> For such scenarios, introduce a new field in paca 'ftrace_disabled',
>> which is checked on ftrace entry before continuing. This field can then
>> be set to a non-zero value to disable/pause ftrace, and reset to zero to
>> resume ftrace.
>>=20
>> Since KVM is the only user for this currently, we guard the
>> ftrace/mcount checks within CONFIG_KVM. This can later be removed
>> if/when there are other users.
>=20
> Why not test HSTATE_IN_GUEST then? Add ftrace_disabled if non-KVM users
> come along.
That's indeed simpler -- thanks for the suggestion!
- Naveen
=
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 1/2] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths
2018-03-19 14:13 ` Steven Rostedt
@ 2018-03-19 18:54 ` Naveen N. Rao
0 siblings, 0 replies; 10+ messages in thread
From: Naveen N. Rao @ 2018-03-19 18:54 UTC (permalink / raw)
To: Steven Rostedt
Cc: Anton Blanchard, Benjamin Herrenschmidt, linuxppc-dev,
Michael Ellerman, Nicholas Piggin, Paul Mackerras, sathnaga
Steven Rostedt wrote:
> On Mon, 19 Mar 2018 14:43:00 +0530
> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
>=20
>> diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S b/arch/power=
pc/kernel/trace/ftrace_64_mprofile.S
>> index 3f3e81852422..fdf702b4df25 100644
>> --- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
>> +++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
>> @@ -60,6 +60,19 @@ _GLOBAL(ftrace_caller)
>> mfxer r10
>> mfcr r11
>> =20
>> +#ifdef CONFIG_KVM
>> + lbz r3, PACA_FTRACE_DISABLED(r13)
>> + cmpdi r3, 0
>> + beq 1f
>> + mflr r3
>> + mtctr r3
>> + REST_GPR(3, r1)
>> + addi r1, r1, SWITCH_FRAME_SIZE
>> + mtlr r0
>> + bctr
>> +1:
>> +#endif
>=20
> I wonder if we should try to move the return out of the fast path (for
> cache reasons), as most of the time the above compare will be true. That
> is:
>=20
> #ifdef CONFIG_KVM
> lbz r3, PACA_FTRACE_DISABLED(r13)
> cmpdi r3, 0
> bne no_trace
> #endif
>=20
> /* rest of ftrace_caller code */
>=20
> /* after ftrace_caller... */
> bctr /* jump after _mcount site */
>=20
> #ifdef CONFIG_KVM
> no_trace:
> mflr r3
> mtctr r3
> REST_GPR(3, r1)
> addi r1, r1, SWITCH_FRAME_SIZE
> mtlr r0
> bctr
> #endif
Thanks, I'll incorporate those changes in my next version.
- Naveen
=
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 1/2] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths
2018-03-19 10:40 ` Nicholas Piggin
2018-03-19 18:53 ` Naveen N. Rao
@ 2018-03-19 22:34 ` Michael Ellerman
2018-03-20 0:05 ` Nicholas Piggin
2018-03-20 11:02 ` Naveen N. Rao
1 sibling, 2 replies; 10+ messages in thread
From: Michael Ellerman @ 2018-03-19 22:34 UTC (permalink / raw)
To: Nicholas Piggin, Naveen N. Rao
Cc: Steven Rostedt, Paul Mackerras, linuxppc-dev,
Benjamin Herrenschmidt, Anton Blanchard, sathnaga
Nicholas Piggin <npiggin@gmail.com> writes:
> On Mon, 19 Mar 2018 14:43:00 +0530
> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
>
>> We have some C code that we call into from real mode where we cannot
>> take any exceptions. Though the C functions themselves are mostly safe,
>> if these functions are traced, there is a possibility that we may take
>> an exception. For instance, in certain conditions, the ftrace code uses
>> WARN(), which uses a 'trap' to do its job.
>>
>> For such scenarios, introduce a new field in paca 'ftrace_disabled',
>> which is checked on ftrace entry before continuing. This field can then
>> be set to a non-zero value to disable/pause ftrace, and reset to zero to
>> resume ftrace.
>>
>> Since KVM is the only user for this currently, we guard the
>> ftrace/mcount checks within CONFIG_KVM. This can later be removed
>> if/when there are other users.
>
> Why not test HSTATE_IN_GUEST then? Add ftrace_disabled if non-KVM users
> come along.
We want to use it for the kexec down path, we've already had bugs there.
So please keep the separate flag and pull it out of #ifdef KVM.
If we're worried about space usage in the paca we can probably
consolidate this and some other things into a flags word.
cheers
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 1/2] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths
2018-03-19 22:34 ` Michael Ellerman
@ 2018-03-20 0:05 ` Nicholas Piggin
2018-03-20 11:02 ` Naveen N. Rao
1 sibling, 0 replies; 10+ messages in thread
From: Nicholas Piggin @ 2018-03-20 0:05 UTC (permalink / raw)
To: Michael Ellerman
Cc: Naveen N. Rao, Steven Rostedt, Paul Mackerras, linuxppc-dev,
Benjamin Herrenschmidt, Anton Blanchard, sathnaga
On Tue, 20 Mar 2018 09:34:43 +1100
Michael Ellerman <mpe@ellerman.id.au> wrote:
> Nicholas Piggin <npiggin@gmail.com> writes:
>
> > On Mon, 19 Mar 2018 14:43:00 +0530
> > "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
> >
> >> We have some C code that we call into from real mode where we cannot
> >> take any exceptions. Though the C functions themselves are mostly safe,
> >> if these functions are traced, there is a possibility that we may take
> >> an exception. For instance, in certain conditions, the ftrace code uses
> >> WARN(), which uses a 'trap' to do its job.
> >>
> >> For such scenarios, introduce a new field in paca 'ftrace_disabled',
> >> which is checked on ftrace entry before continuing. This field can then
> >> be set to a non-zero value to disable/pause ftrace, and reset to zero to
> >> resume ftrace.
> >>
> >> Since KVM is the only user for this currently, we guard the
> >> ftrace/mcount checks within CONFIG_KVM. This can later be removed
> >> if/when there are other users.
> >
> > Why not test HSTATE_IN_GUEST then? Add ftrace_disabled if non-KVM users
> > come along.
>
> We want to use it for the kexec down path, we've already had bugs there.
>
> So please keep the separate flag and pull it out of #ifdef KVM.
Okay that's fine.
> If we're worried about space usage in the paca we can probably
> consolidate this and some other things into a flags word.
I'm not too concerned about some more u8 flags.
Thanks,
Nick
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 1/2] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths
2018-03-19 22:34 ` Michael Ellerman
2018-03-20 0:05 ` Nicholas Piggin
@ 2018-03-20 11:02 ` Naveen N. Rao
1 sibling, 0 replies; 10+ messages in thread
From: Naveen N. Rao @ 2018-03-20 11:02 UTC (permalink / raw)
To: Michael Ellerman, Nicholas Piggin
Cc: Anton Blanchard, Benjamin Herrenschmidt, linuxppc-dev,
Paul Mackerras, Steven Rostedt, sathnaga
Michael Ellerman wrote:
> Nicholas Piggin <npiggin@gmail.com> writes:
>=20
>> On Mon, 19 Mar 2018 14:43:00 +0530
>> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
>>
>>> We have some C code that we call into from real mode where we cannot
>>> take any exceptions. Though the C functions themselves are mostly safe,
>>> if these functions are traced, there is a possibility that we may take
>>> an exception. For instance, in certain conditions, the ftrace code uses
>>> WARN(), which uses a 'trap' to do its job.
>>>=20
>>> For such scenarios, introduce a new field in paca 'ftrace_disabled',
>>> which is checked on ftrace entry before continuing. This field can then
>>> be set to a non-zero value to disable/pause ftrace, and reset to zero t=
o
>>> resume ftrace.
>>>=20
>>> Since KVM is the only user for this currently, we guard the
>>> ftrace/mcount checks within CONFIG_KVM. This can later be removed
>>> if/when there are other users.
>>
>> Why not test HSTATE_IN_GUEST then? Add ftrace_disabled if non-KVM users
>> come along.
>=20
> We want to use it for the kexec down path, we've already had bugs there.
I had looked at kexec and we seem to be disabling ftrace in=20
machine_kexec(). Has that been problematic?
I didn't actually realize that you wanted to use this in kexec path as=20
well.
>=20
> So please keep the separate flag and pull it out of #ifdef KVM.
Sure.
- Naveen
=
^ permalink raw reply [flat|nested] 10+ messages in thread
end of thread, other threads:[~2018-03-20 11:03 UTC | newest]
Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-03-19 9:12 [PATCH 0/2] Disable ftrace during kvm guest entry/exit Naveen N. Rao
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2018-03-19 10:40 ` Nicholas Piggin
2018-03-19 18:53 ` Naveen N. Rao
2018-03-19 22:34 ` Michael Ellerman
2018-03-20 0:05 ` Nicholas Piggin
2018-03-20 11:02 ` Naveen N. Rao
2018-03-19 14:13 ` Steven Rostedt
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