linux-kernel - [PATCH 6/9] vdso: Only use MAP_DROPPABLE when VM

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Message-ID: <712424314ffe0bd65b603925ca1283e7d2a3745f.1723817900.git.christophe.leroy@csgroup.eu>
Date: Fri, 16 Aug 2024 16:36:53 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Naveen N Rao <naveen@...nel.org>,
	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>,
	"Theodore Ts'o" <tytso@....edu>,
	"Jason A. Donenfeld" <Jason@...c4.com>,
	Andy Lutomirski <luto@...nel.org>,
	Vincenzo Frascino <vincenzo.frascino@....com>,
	Arnd Bergmann <arnd@...db.de>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>,
	linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org,
	linux-arch@...r.kernel.org
Subject: [PATCH 6/9] vdso: Only use MAP_DROPPABLE when VM_DROPPABLE exists

Commit 9651fcedf7b9 ("mm: add MAP_DROPPABLE for designating always
lazily freeable mappings") only adds MAP_DROPPABLE for 64 bits
architectures, so don't use it on 32 bits as it leads to ENOTSUPP
on mmap().

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 lib/vdso/getrandom.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/lib/vdso/getrandom.c b/lib/vdso/getrandom.c
index 425a422651de..11ba6dbf3b5e 100644
--- a/lib/vdso/getrandom.c
+++ b/lib/vdso/getrandom.c
@@ -78,7 +78,11 @@ __cvdso_getrandom_data(const struct vdso_rng_data *rng_info, void *buffer, size_
 
 		params->size_of_opaque_state = sizeof(*state);
 		params->mmap_prot = PROT_READ | PROT_WRITE;
-		params->mmap_flags = MAP_DROPPABLE | MAP_ANONYMOUS;
+		if (IS_ENABLED(CONFIG_64BIT))
+			params->mmap_flags = MAP_DROPPABLE | MAP_ANONYMOUS;
+		else
+			params->mmap_flags = MAP_PRIVATE | MAP_ANONYMOUS;
+
 		for (i = 0; i < ARRAY_SIZE(params->reserved); i++)
 			params->reserved[i] = 0;
 
-- 
2.44.0