[PATCH] thp: fix PARAVIRT x86 32bit noPAE

[Andrea Arcangeli <aarcange@redhat.com>]

I reproduced your 32bit x86 problem with an initramfs with a hugepage
benchmark placed as /init inside KVM (not exactly an extensive test
but it was trivial to reproduce). I tested below fix with HIGHMEM4G
and HIGHMEM64G with PARAVIRT=y (and verified setting PARAVIRT=n fixed
it, in other email Minchan also verified that setting HIGHMEM64G=y
also fixed it, to confirm my theory the problem was the below #ifdef).

The stress test reaches exit() successfully now (before the fix it
crashed in out_of_memory() instead of do_exit as expected):

NMI watchdog disabled for cpu0: unable to create perf event: -2
�Kernel panic - not syncing: Attempted to kill init!
Pid: 1, comm: init Not tainted 2.6.37+ #17
Call Trace:
 [<c14351d2>] ? panic+0x57/0x161
 [<c107439b>] ? trace_hardirqs_on+0xb/0x10
 [<c1045321>] ? do_exit+0x6b1/0x6e0
 [<c10728ab>] ? trace_hardirqs_off+0xb/0x10
 [<c1045389>] ? do_group_exit+0x39/0xa0
 [<c1045403>] ? sys_exit_group+0x13/0x20
 [<c1002d9c>] ? sysenter_do_call+0x12/0x3c
QEMU 0.12.1 monitor - type 'help' for more information
(qemu) quit

====
Subject: thp: fix PARAVIRT x86 32bit noPAE

From: Andrea Arcangeli <aarcange@redhat.com>

This fixes TRANSPARENT_HUGEPAGE=y with PARAVIRT=y and HIGHMEM64=n.

The #ifdef that this patch removes was erratically introduced to fix a build
error for noPAE (where pmd.pmd doesn't exist). So then the kernel built but it
failed at runtime because set_pmd_at was a noop. This will correct it by
enabling set_pmd_at for noPAE mode too.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 2071a8b..ebbc4d8 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -558,13 +558,12 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
 static inline void set_pmd_at(struct mm_struct *mm, unsigned long addr,
 			      pmd_t *pmdp, pmd_t pmd)
 {
-#if PAGETABLE_LEVELS >= 3
 	if (sizeof(pmdval_t) > sizeof(long))
 		/* 5 arg words */
 		pv_mmu_ops.set_pmd_at(mm, addr, pmdp, pmd);
 	else
-		PVOP_VCALL4(pv_mmu_ops.set_pmd_at, mm, addr, pmdp, pmd.pmd);
-#endif
+		PVOP_VCALL4(pv_mmu_ops.set_pmd_at, mm, addr, pmdp,
+			    native_pmd_val(pmd));
 }
 #endif