Re: Today's -current no longer boots on my amd64 machine

[Jean-Yves Migeon <jeanyves.migeon%free.fr@localhost>]

On 04/20/10 02:03, Joerg Sonnenberger wrote:
> On Tue, Apr 20, 2010 at 01:52:30AM +0200, Jean-Yves Migeon wrote:
> > Yep I know, and I also have to check about the CPUID_NOX feature of cpuid.
>
> I'm not sure that it going to work either. In fact, I am quite sure it
> doesn't. You will get a GPF if accessing a page with the NX bit set if
> the feature is not active.

Yeah, I saw that yesterday in the AMD docs.

The previous patch sets the EFER_NXE bit after having enabled paging and 
long mode.

I can move it closer to the %cr0 assignement, but not much; the 
cpu_feature variable is in 64 bit code, and before the ljmp to 
mp_trampoline_end, we are still in 32 bit code; this won't link.

FWIW, the #GP occuring without the patch is due to the idlelwp struct 
being allocated in the slow path of a pool_cache, and is very likely to 
be marked as NX by BP.

I can move it above the cpu_starting busy wait loop, might give some 
delay to the secondary CPU.

Index: sys/arch/amd64/amd64/mptramp.S
===================================================================
RCS file: /cvsroot/src/sys/arch/amd64/amd64/mptramp.S,v
retrieving revision 1.11
diff -u -u -r1.11 mptramp.S
--- sys/arch/amd64/amd64/mptramp.S      18 Apr 2010 23:47:50 -0000      1.11
+++ sys/arch/amd64/amd64/mptramp.S      20 Apr 2010 07:26:33 -0000
@@ -217,6 +217,18 @@
        
 _C_LABEL(cpu_spinup_trampoline_end):   #end of code copied to MP_TRAMPOLINE
 1:
+       /*
+        * Without EFER_NXE enabled on the CPU, a set NX bit will raise
+        * a #GP. Avoid that by setting the NXE feature now.
+        */
+       movl    _C_LABEL(cpu_feature)+2*4,%eax  /* cpu_feature[2] */
+       andl    $CPUID_NOX,%eax
+       jz      1f
+       movl    $MSR_EFER,%ecx
+       rdmsr
+       orl     $EFER_NXE,%eax  /* enable No-Execute feature */
+       wrmsr
+
        /* Don't touch lapic until BP has done init sequence. */
        movq    _C_LABEL(cpu_starting),%rdi
        pause


--
Jean-Yves Migeon
jeanyves.migeon%free.fr@localhost