The patch below eliminates a case of boot_cpu_data corruption
on SMP x86 machines. This was first observed on SMP Athlons,
but it also affects SMP Intel boxes in a less serious way.
When the secondary processors boot and execute head.S:checkCPUtype,
the code performs a 32-bit write of a small constant to the
byte-sized variable boot_cpu_data.x86 (X86 in head.S). Since the
write is 32-bit, it also writes zeros to the following 3 bytes,
which clobbers the x86_vendor, x86_model, and x86_mask fields
previously set up by check_bugs()'s call to identify_cpu().
Thus, after smp_init(), boot_cpu_data will _always_ identify
the CPU as an Intel (X86_VENDOR_INTEL == 0 in processor.h) with
model 0 and stepping 0.
The effect in standard kernels is not catastrophic, since:
(a) most SMP x86 boxes are Intel
(b) most uses of x86_vendor occur before smp_init() or reference
the SMP cpu_data[] array
(c) most post-boot references to boot_cpu_data occur in the
cpu_has_XXX macros which only read the x86_capability[] array
However, third-party extensions (like my x86 performance-monitoring
conters driver) can get seriously confused by this mis-identification.
The patch is for 2.4.19-pre3, but it also applies to 2.5.6 and
2.2.21rc1. Please apply.
/Mikael
--- linux-2.4.19-pre3/arch/i386/kernel/head.S.~1~ Tue Feb 26 13:26:56 2002
+++ linux-2.4.19-pre3/arch/i386/kernel/head.S Thu Mar 14 16:20:57 2002
@@ -178,7 +178,7 @@
* we don't need to preserve eflags.
*/
- movl $3,X86 # at least 386
+ movb $3,X86 # at least 386
pushfl # push EFLAGS
popl %eax # get EFLAGS
movl %eax,%ecx # save original EFLAGS
@@ -191,7 +191,7 @@
andl $0x40000,%eax # check if AC bit changed
je is386
- movl $4,X86 # at least 486
+ movb $4,X86 # at least 486
movl %ecx,%eax
xorl $0x200000,%eax # check ID flag
pushl %eax
-
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This archive was generated by hypermail 2b29 : Fri Mar 15 2002 - 22:00:18 EST