From: Aaron Lu <aaron.lu@intel.com>
To: Dave Hansen <dave.hansen@intel.com>,
Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: Song Liu <song@kernel.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: [RFC PATCH 1/4] x86/mm/cpa: restore global bit when page is present
Date: Mon, 8 Aug 2022 22:56:46 +0800 [thread overview]
Message-ID: <20220808145649.2261258-2-aaron.lu@intel.com> (raw)
In-Reply-To: <20220808145649.2261258-1-aaron.lu@intel.com>
For configs that don't have PTI enabled or cpus that don't need
meltdown mitigation, current kernel can lose GLOBAL bit after a page
goes through a cycle of present -> not present -> present.
It happened like this(__vunmap() does this in vm_remove_mappings()):
original page protection: 0x8000000000000163 (NX/G/D/A/RW/P)
set_memory_np(page, 1): 0x8000000000000062 (NX/D/A/RW) lose G and P
set_memory_p(pagem 1): 0x8000000000000063 (NX/D/A/RW/P) restored P
In the end, this page's protection no longer has Global bit set and this
would create problem for this merge small mapping feature.
For this reason, restore Global bit for systems that do not have PTI
enabled if page is present.
(pgprot_clear_protnone_bits() deserves a better name if this patch is
acceptible but first, I would like to get some feedback if this is the
right way to solve this so I didn't bother with the name yet)
Signed-off-by: Aaron Lu <aaron.lu@intel.com>
---
arch/x86/mm/pat/set_memory.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 1abd5438f126..33657a54670a 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -758,6 +758,8 @@ static pgprot_t pgprot_clear_protnone_bits(pgprot_t prot)
*/
if (!(pgprot_val(prot) & _PAGE_PRESENT))
pgprot_val(prot) &= ~_PAGE_GLOBAL;
+ else
+ pgprot_val(prot) |= _PAGE_GLOBAL & __default_kernel_pte_mask;
return prot;
}
--
2.37.1
next prev parent reply other threads:[~2022-08-08 14:57 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-08 14:56 [RFC PATCH 0/4] x86/mm/cpa: merge small mappings whenever possible Aaron Lu
2022-08-08 14:56 ` Aaron Lu [this message]
2022-08-11 5:21 ` [RFC PATCH 1/4] x86/mm/cpa: restore global bit when page is present Hyeonggon Yoo
2022-08-11 8:16 ` Lu, Aaron
2022-08-11 11:30 ` Hyeonggon Yoo
2022-08-11 12:28 ` Aaron Lu
2022-08-08 14:56 ` [RFC PATCH 2/4] x86/mm/cpa: merge splitted direct mapping when possible Aaron Lu
2022-08-08 14:56 ` [RFC PATCH 3/4] x86/mm/cpa: add merge event counter Aaron Lu
2022-08-08 14:56 ` [TEST NOT_FOR_MERGE 4/4] x86/mm/cpa: add a test interface to split direct map Aaron Lu
2022-08-09 10:04 ` [RFC PATCH 0/4] x86/mm/cpa: merge small mappings whenever possible Kirill A. Shutemov
2022-08-09 14:58 ` Aaron Lu
2022-08-09 17:56 ` Kirill A. Shutemov
2022-08-11 4:50 ` Hyeonggon Yoo
2022-08-11 7:50 ` Lu, Aaron
2022-08-13 16:05 ` Mike Rapoport
2022-08-16 6:33 ` Aaron Lu
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