linux-kernel - [RFC PATCH 08/10] mm: hugetlb: disable CMA if liveupdate is enabled

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Message-ID: <20251206230222.853493-9-pratyush@kernel.org>
Date: Sun,  7 Dec 2025 00:02:18 +0100
From: Pratyush Yadav <pratyush@...nel.org>
To: Pasha Tatashin <pasha.tatashin@...een.com>,
	Mike Rapoport <rppt@...nel.org>,
	Pratyush Yadav <pratyush@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...nel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Jonathan Corbet <corbet@....net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Muchun Song <muchun.song@...ux.dev>,
	Oscar Salvador <osalvador@...e.de>,
	Alexander Graf <graf@...zon.com>,
	David Matlack <dmatlack@...gle.com>,
	David Rientjes <rientjes@...gle.com>,
	Jason Gunthorpe <jgg@...dia.com>,
	Samiullah Khawaja <skhawaja@...gle.com>,
	Vipin Sharma <vipinsh@...gle.com>,
	Zhu Yanjun <yanjun.zhu@...ux.dev>
Cc: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	linux-doc@...r.kernel.org,
	kexec@...ts.infradead.org
Subject: [RFC PATCH 08/10] mm: hugetlb: disable CMA if liveupdate is enabled

Hugetlb live update support does not yet work with CMA. Print a warning
and disable CMA if the config for live updating hugetlb is enabled, and
liveupdate is enabled at runtime.

Signed-off-by: Pratyush Yadav <pratyush@...nel.org>
---
 kernel/liveupdate/Kconfig | 3 +++
 mm/hugetlb_cma.c          | 7 +++++++
 2 files changed, 10 insertions(+)

diff --git a/kernel/liveupdate/Kconfig b/kernel/liveupdate/Kconfig
index 86e76aed8a93..4676fea6d8a6 100644
--- a/kernel/liveupdate/Kconfig
+++ b/kernel/liveupdate/Kconfig
@@ -82,6 +82,9 @@ config LIVEUPDATE_HUGETLB
 	  use hugetlb memfd to back VM memory, or for other user workloads needing
 	  to live update huge pages.
 
+	  Enabling this config disables CMA for hugetlb pages. It is not yet
+	  supported with live update.
+
 	  If unsure, say N.
 
 endmenu
diff --git a/mm/hugetlb_cma.c b/mm/hugetlb_cma.c
index e8e4dc7182d5..fa3bb776c0d2 100644
--- a/mm/hugetlb_cma.c
+++ b/mm/hugetlb_cma.c
@@ -4,6 +4,7 @@
 #include <linux/cma.h>
 #include <linux/compiler.h>
 #include <linux/mm_inline.h>
+#include <linux/liveupdate.h>
 
 #include <asm/page.h>
 #include <asm/setup.h>
@@ -152,6 +153,12 @@ void __init hugetlb_cma_reserve(int order)
 	if (!hugetlb_cma_size)
 		return;
 
+	if (IS_ENABLED(CONFIG_LIVEUPDATE_HUGETLB) && liveupdate_enabled()) {
+		pr_warn("HugeTLB: CMA not supported with live update. Falling back to pre-allocating pages.\n");
+		hugetlb_cma_size = 0;
+		return;
+	}
+
 	hugetlb_bootmem_set_nodes();
 
 	for (nid = 0; nid < MAX_NUMNODES; nid++) {
-- 
2.43.0