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Message-Id: <1383876946-2396-66-git-send-email-kamal@canonical.com> Date: Thu, 7 Nov 2013 18:15:20 -0800 From: Kamal Mostafa <kamal@...onical.com> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org, kernel-team@...ts.ubuntu.com Cc: Helge Deller <deller@....de>, John David Anglin <dave.anglin@...l.net>, Kamal Mostafa <kamal@...onical.com> Subject: [PATCH 3.8 65/91] parisc: Do not crash 64bit SMP kernels on machines with >= 4GB RAM 3.8.13.13 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Helge Deller <deller@....de> commit 54e181e073fc1415e41917d725ebdbd7de956455 upstream. Since the beginning of the parisc-linux port, sometimes 64bit SMP kernels were not able to bring up other CPUs than the monarch CPU and instead crashed the kernel. The reason was unclear, esp. since it involved various machines (e.g. J5600, J6750 and SuperDome). Testing showed, that those crashes didn't happened when less than 4GB were installed, or if a 32bit Linux kernel was booted. In the end, the fix for those SMP problems is trivial: During the early phase of the initialization of the CPUs, including the monarch CPU, the PDC_PSW firmware function to enable WIDE (=64bit) mode is called. It's documented that this firmware function may clobber various registers, and one one of those possibly clobbered registers is %cr30 which holds the task thread info pointer. Now, if %cr30 would always have been clobbered, then this bug would have been detected much earlier. But lots of testing finally showed, that - at least for %cr30 - on some machines only the upper 32bits of the 64bit register suddenly turned zero after the firmware call. So, after finding the root cause, the explanation for the various crashes became clear: - On 32bit SMP Linux kernels all upper 32bit were zero, so we didn't faced this problem. - Monarch CPUs in 64bit mode always booted sucessfully, because the inital task thread info pointer was below 4GB. - Secondary CPUs booted sucessfully on machines with less than 4GB RAM because the upper 32bit were zero anyay. - Secondary CPus failed to boot if we had more than 4GB RAM and the task thread info pointer was located above the 4GB boundary. Finally, the patch to fix this problem is trivial by saving the %cr30 register before the firmware call and restoring it afterwards. Signed-off-by: Helge Deller <deller@....de> Signed-off-by: John David Anglin <dave.anglin@...l.net> Signed-off-by: Helge Deller <deller@....de> Signed-off-by: Kamal Mostafa <kamal@...onical.com> --- arch/parisc/kernel/head.S | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/parisc/kernel/head.S b/arch/parisc/kernel/head.S index 37aabd7..d2d5825 100644 --- a/arch/parisc/kernel/head.S +++ b/arch/parisc/kernel/head.S @@ -195,6 +195,8 @@ common_stext: ldw MEM_PDC_HI(%r0),%r6 depd %r6, 31, 32, %r3 /* move to upper word */ + mfctl %cr30,%r6 /* PCX-W2 firmware bug */ + ldo PDC_PSW(%r0),%arg0 /* 21 */ ldo PDC_PSW_SET_DEFAULTS(%r0),%arg1 /* 2 */ ldo PDC_PSW_WIDE_BIT(%r0),%arg2 /* 2 */ @@ -203,6 +205,8 @@ common_stext: copy %r0,%arg3 stext_pdc_ret: + mtctl %r6,%cr30 /* restore task thread info */ + /* restore rfi target address*/ ldd TI_TASK-THREAD_SZ_ALGN(%sp), %r10 tophys_r1 %r10 -- 1.8.1.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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