linux-kernel - [PATCH v3 02/13] x86/xen: simplify flush_lazy

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Message-ID: <20251015082727.2395128-3-kevin.brodsky@arm.com>
Date: Wed, 15 Oct 2025 09:27:16 +0100
From: Kevin Brodsky <kevin.brodsky@....com>
To: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org,
	Kevin Brodsky <kevin.brodsky@....com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Andreas Larsson <andreas@...sler.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Borislav Petkov <bp@...en8.de>,
	Catalin Marinas <catalin.marinas@....com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	David Hildenbrand <david@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	"H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...hat.com>,
	Jann Horn <jannh@...gle.com>,
	Juergen Gross <jgross@...e.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
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	Suren Baghdasaryan <surenb@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vlastimil Babka <vbabka@...e.cz>,
	Will Deacon <will@...nel.org>,
	Yeoreum Yun <yeoreum.yun@....com>,
	linux-arm-kernel@...ts.infradead.org,
	linuxppc-dev@...ts.ozlabs.org,
	sparclinux@...r.kernel.org,
	xen-devel@...ts.xenproject.org,
	x86@...nel.org
Subject: [PATCH v3 02/13] x86/xen: simplify flush_lazy_mmu()

arch_flush_lazy_mmu_mode() is called when outstanding batched
pgtable operations must be completed immediately. There should
however be no need to leave and re-enter lazy MMU completely. The
only part of that sequence that we really need is xen_mc_flush();
call it directly.

While at it, we can also avoid preempt_disable() if we are not
in lazy MMU mode - xen_get_lazy_mode() should tolerate preemption.

Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>
---
 arch/x86/xen/mmu_pv.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
index 2a4a8deaf612..dcb7b0989c32 100644
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -2137,14 +2137,11 @@ static void xen_enter_lazy_mmu(void)
 
 static void xen_flush_lazy_mmu(void)
 {
-	preempt_disable();
-
 	if (xen_get_lazy_mode() == XEN_LAZY_MMU) {
-		arch_leave_lazy_mmu_mode();
-		arch_enter_lazy_mmu_mode();
+		preempt_disable();
+		xen_mc_flush();
+		preempt_enable();
 	}
-
-	preempt_enable();
 }
 
 static void __init xen_post_allocator_init(void)
-- 
2.47.0