Re: Kernel 4.1.28: Update TM user feature bits in scan_features()

Christian Zigotzky [off-list ref] writes:

Hi All,

I tried to compile the kernel 4.1.28 today. Unfortunately it doesn't 
compile because of an undeclared variable PPC_FEATURE2_HTM_NOSC_COMP.

Error message:

   CHK     include/config/kernel.release
   CHK     include/generated/uapi/linux/version.h
   CHK     include/generated/utsrelease.h
   CHK     include/generated/bounds.h
   CHK     include/generated/asm-offsets.h
   CALL    scripts/checksyscalls.sh
   CHK     include/generated/compile.h
   CALL    arch/powerpc/kernel/systbl_chk.sh
   CC      arch/powerpc/kernel/prom.o
arch/powerpc/kernel/prom.c:170:25: error: 'PPC_FEATURE2_HTM_NOSC_COMP' 
undeclared here (not in a function)
    PPC_FEATURE2_HTM_COMP|PPC_FEATURE2_HTM_NOSC_COMP, 22, 0, 0},
                          ^
make[1]: *** [arch/powerpc/kernel/prom.o] Error 1
make: *** [arch/powerpc/kernel] Error 2

---

Commit:

f49eb503f0f9ab66874a81992b14249a1c59b6ad
Author: Anton Blanchard [off-list ref]
Date:   Fri Apr 15 12:08:19 2016 +1000

     powerpc: Update TM user feature bits in scan_features()

     [ Upstream commit 4705e02498d6d5a7ab98dfee9595cd5e91db2017 ]

     We need to update the user TM feature bits (PPC_FEATURE2_HTM and
     PPC_FEATURE2_HTM) to mirror what we do with the kernel TM feature
     bit.

     At the moment, if firmware reports TM is not available we turn off
     the kernel TM feature bit but leave the userspace ones on. Userspace
     thinks it can execute TM instructions and it dies trying.

     This (together with a QEMU patch) fixes PR KVM, which doesn't currently
     support TM.

     Signed-off-by: Anton Blanchard [off-list ref]
     Cc: stable@vger.kernel.org
     Signed-off-by: Michael Ellerman [off-list ref]
     Signed-off-by: Sasha Levin [off-list ref]

---

PPC_FEATURE2_HTM_NOSC_COMP isn't defined or doesn't exist in the 
following files:

Thanks.

arch/powerpc/include/asm/cputable.h
arch/powerpc/kernel/cputable.c
arch/powerpc/include/uapi/asm/tm.h

That means the following patches aren't included in the 4.1.28 source code:

Sorry that's the wrong fix.

PPC_FEATURE2_HTM_NOSC indicates the presence of a certain kernel
behaviour, which has *not* been backported to 4.1.

The right fix is just to remove the reference to PPC_FEATURE2_HTM_NOSC
in 4.1.28.

eg:

diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 28dbbb0d12c4..9b19d96e9562 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c

@@ -166,8 +166,7 @@ static struct ibm_pa_feature {
 	 * we don't want to turn on TM here, so we use the *_COMP versions
 	 * which are 0 if the kernel doesn't support TM.
 	 */
-	{CPU_FTR_TM_COMP, 0, 0,
-	 PPC_FEATURE2_HTM_COMP|PPC_FEATURE2_HTM_NOSC_COMP, 22, 0, 0},
+	{CPU_FTR_TM_COMP, 0, 0, PPC_FEATURE2_HTM_COMP, 22, 0, 0},
 };
 
 static void __init scan_features(unsigned long node, const unsigned char *ftrs,

cheers