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Subject[PATCH 21 of 24] xen: allow set_pte_at on init_mm to be lockless
Date
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The usual pagetable locking protocol doesn't seem to apply to updates
to init_mm, so don't rely on preemption being disabled in xen_set_pte_at
on init_mm.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
---
arch/x86/xen/mmu.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -156,6 +156,10 @@
void xen_set_pte_at(struct mm_struct *mm, unsigned long addr,
pte_t *ptep, pte_t pteval)
{
+ /* updates to init_mm may be done without lock */
+ if (mm == &init_mm)
+ preempt_disable();
+
if (mm == current->mm || mm == &init_mm) {
if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_MMU) {
struct multicall_space mcs;
@@ -163,12 +167,16 @@

MULTI_update_va_mapping(mcs.mc, addr, pteval, 0);
xen_mc_issue(PARAVIRT_LAZY_MMU);
- return;
+ goto out;
} else
if (HYPERVISOR_update_va_mapping(addr, pteval, 0) == 0)
- return;
+ goto out;
}
xen_set_pte(ptep, pteval);
+
+out:
+ if (mm == &init_mm)
+ preempt_enable();
}

pteval_t xen_pte_val(pte_t pte)



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