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x86/xen: Tolerate nested XEN_LAZY_MMU entering/leaving

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With the support of nested lazy mmu sections it can happen that
arch_enter_lazy_mmu_mode() is being called twice without a call of
arch_leave_lazy_mmu_mode() in between, as the lazy_mmu_*() helpers
are not disabling preemption when checking for nested lazy mmu
sections.

This is a problem when running as a Xen PV guest, as
xen_enter_lazy_mmu() and xen_leave_lazy_mmu() don't tolerate this
case.

Fix that in xen_enter_lazy_mmu() and xen_leave_lazy_mmu() in order
not to hurt all other lazy mmu mode users.

Fixes: 291b3abed6 ("x86/xen: use lazy_mmu_state when context-switching")
Tested-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Message-ID: <20260508143933.493013-1-jgross@suse.com>
This commit is contained in:
Juergen Gross
2026-05-08 16:39:33 +02:00
parent 28e03f78e6
commit 4594437880
1 changed files with 6 additions and 2 deletions
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8
arch/x86/xen/mmu_pv.c
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@@ -2145,7 +2145,10 @@ static void xen_set_fixmap(unsigned idx, phys_addr_t phys, pgprot_t prot)
static void xen_enter_lazy_mmu(void)
{
enter_lazy(XEN_LAZY_MMU);
preempt_disable();
if (xen_get_lazy_mode() != XEN_LAZY_MMU)
enter_lazy(XEN_LAZY_MMU);
preempt_enable();
}
static void xen_flush_lazy_mmu(void)
@@ -2182,7 +2185,8 @@ static void xen_leave_lazy_mmu(void)
{
preempt_disable();
xen_mc_flush();
leave_lazy(XEN_LAZY_MMU);
if (xen_get_lazy_mode() != XEN_LAZY_NONE)
leave_lazy(XEN_LAZY_MMU);
preempt_enable();
}