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Peter Anvin" , xen-devel@lists.xenproject.org Subject: [PATCH] x86/xen: Tolerate nested XEN_LAZY_MMU entering/leaving Date: Fri, 8 May 2026 16:39:33 +0200 Message-ID: <20260508143933.493013-1-jgross@suse.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Level: X-Spamd-Result: default: False [-2.80 / 50.00]; BAYES_HAM(-3.00)[100.00%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_MISSING_CHARSET(0.50)[]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_COUNT_TWO(0.00)[2]; RCPT_COUNT_TWELVE(0.00)[12]; FUZZY_RATELIMITED(0.00)[rspamd.com]; DKIM_SIGNED(0.00)[suse.com:s=susede1]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; TO_DN_SOME(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.com:mid,suse.com:email,imap1.dmz-prg2.suse.org:helo] X-Spam-Flag: NO X-Spam-Score: -2.80 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") Signed-off-by: Juergen Gross --- 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(); } -- 2.54.0