From 4594437880ce347ac8438758fd91543f70da1aa9 Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Fri, 8 May 2026 16:39:33 +0200 Subject: [PATCH] x86/xen: Tolerate nested XEN_LAZY_MMU entering/leaving MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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: 291b3abed657 ("x86/xen: use lazy_mmu_state when context-switching") Tested-by: Marek Marczykowski-Górecki Signed-off-by: Juergen Gross Message-ID: <20260508143933.493013-1-jgross@suse.com> --- arch/x86/xen/mmu_pv.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c index c80d0058efd1..3eee5f84f8a7 100644 --- a/arch/x86/xen/mmu_pv.c +++ b/arch/x86/xen/mmu_pv.c @@ -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(); }