| Message ID | 18732.40814.991329.362635@cargo.ozlabs.ibm.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
On Wednesday 26 November 2008, Paul Mackerras wrote: > This fixes it by moving the clearing of CR0.SO to after the > ACCOUNT_CPU_USER_ENTRY call in the system call entry path. Thanks for taking care of this! > Signed-off-by: Paul Mackerras <paulus@samba.org> Acked-by: Arnd Bergmann <arnd@arndb.de>
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S index e6d5284..9d80f55 100644 --- a/arch/powerpc/kernel/entry_64.S +++ b/arch/powerpc/kernel/entry_64.S @@ -57,12 +57,12 @@ system_call_common: beq- 1f ld r1,PACAKSAVE(r13) 1: std r10,0(r1) - crclr so std r11,_NIP(r1) std r12,_MSR(r1) std r0,GPR0(r1) std r10,GPR1(r1) ACCOUNT_CPU_USER_ENTRY(r10, r11) + crclr so std r2,GPR2(r1) std r3,GPR3(r1) std r4,GPR4(r1)
It turns out that on Cell, on a kernel with CONFIG_VIRT_CPU_ACCOUNTING = y, if a program sets the SO (summary overflow) bit in the XER and then does a system call, the SO bit in CR0 will be set on return regardless of whether the system call detected an error. Since CR0.SO is used as the error indication from the system call, this means that all system calls appear to fail. The reason is that the workaround for the timebase bug on Cell uses a compare instruction. With CONFIG_VIRT_CPU_ACCOUNTING = y, the ACCOUNT_CPU_USER_ENTRY macro reads the timebase, so we end up doing a compare instruction, which copies XER.SO to CR0.SO. Since we were doing this in the system call entry patch after clearing CR0.SO but before saving the CR, this meant that the saved CR image had CR0.SO set if XER.SO was set on entry. This fixes it by moving the clearing of CR0.SO to after the ACCOUNT_CPU_USER_ENTRY call in the system call entry path. Signed-off-by: Paul Mackerras <paulus@samba.org> ---