linux-kernel - [RFC v2 12/13] book3s64/hash: Disable kfence if not early init

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Message-ID: <43e00322c775645a251c4526484d5bc61c62850d.1726571179.git.ritesh.list@gmail.com>
Date: Thu, 19 Sep 2024 08:26:10 +0530
From: "Ritesh Harjani (IBM)" <ritesh.list@...il.com>
To: linuxppc-dev@...ts.ozlabs.org
Cc: Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Hari Bathini <hbathini@...ux.ibm.com>,
	"Aneesh Kumar K . V" <aneesh.kumar@...nel.org>,
	Donet Tom <donettom@...ux.vnet.ibm.com>,
	Pavithra Prakash <pavrampu@...ux.vnet.ibm.com>,
	Nirjhar Roy <nirjhar@...ux.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	kasan-dev@...glegroups.com,
	"Ritesh Harjani (IBM)" <ritesh.list@...il.com>
Subject: [RFC v2 12/13] book3s64/hash: Disable kfence if not early init

Enable kfence on book3s64 hash only when early init is enabled.
This is because, kfence could cause the kernel linear map to be mapped
at PAGE_SIZE level instead of 16M (which I guess we don't want).

Also currently there is no way to -
1. Make multiple page size entries for the SLB used for kernel linear
   map.
2. No easy way of getting the hash slot details after the page table
   mapping for kernel linear setup. So even if kfence allocate the
   pool in late init, we won't be able to get the hash slot details in
   kfence linear map.

Thus this patch disables kfence on hash if kfence early init is not
enabled.

Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
---
 arch/powerpc/mm/book3s64/hash_utils.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
index 53e6f3a524eb..b6da25719e37 100644
--- a/arch/powerpc/mm/book3s64/hash_utils.c
+++ b/arch/powerpc/mm/book3s64/hash_utils.c
@@ -410,6 +410,8 @@ static phys_addr_t kfence_pool;
 
 static inline void hash_kfence_alloc_pool(void)
 {
+	if (!kfence_early_init_enabled())
+		goto err;
 
 	// allocate linear map for kfence within RMA region
 	linear_map_kf_hash_count = KFENCE_POOL_SIZE >> PAGE_SHIFT;
@@ -1074,7 +1076,7 @@ static void __init htab_init_page_sizes(void)
 	bool aligned = true;
 	init_hpte_page_sizes();
 
-	if (!debug_pagealloc_enabled_or_kfence()) {
+	if (!debug_pagealloc_enabled() && !kfence_early_init_enabled()) {
 		/*
 		 * Pick a size for the linear mapping. Currently, we only
 		 * support 16M, 1M and 4K which is the default
-- 
2.46.0