linux-kernel - [PATCH] x86: mm: Do not use set_{pud,pmd}

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Date:   Mon, 8 Apr 2019 19:11:21 +0000
From:   "Singh, Brijesh" <brijesh.singh@....com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
CC:     "Singh, Brijesh" <brijesh.singh@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>
Subject: [PATCH] x86: mm: Do not use set_{pud,pmd}_safe when splitting the
 large page

The following commit 0a9fe8ca844d ("x86/mm: Validate kernel_physical_mapping_init()
PTE population") triggers the below warning in the SEV guest.

WARNING: CPU: 0 PID: 0 at arch/x86/include/asm/pgalloc.h:87 phys_pmd_init+0x30d/0x386
Call Trace:
 kernel_physical_mapping_init+0xce/0x259
 early_set_memory_enc_dec+0x10f/0x160
 kvm_smp_prepare_boot_cpu+0x71/0x9d
 start_kernel+0x1c9/0x50b
 secondary_startup_64+0xa4/0xb0

The SEV guest calls kernel_physical_mapping_init() to clear the encryption
mask from an existing mapping. While clearing the encryption mask
kernel_physical_mapping_init() splits the large pages into the smaller.
To split the page, the kernel_physical_mapping_init() allocates a new page
and updates the existing entry. The set_{pud,pmd}_safe triggers warning
when updating the entry with page in the present state. We should use the
set_{pud,pmd} when updating an existing entry with the new entry.

Updating an entry will also requires a TLB flush. Currently the caller
(early_set_memory_enc_dec()) is taking care of issuing the TLB flushes.

Signed-off-by: Brijesh Singh <brijesh.singh@....com>
Fixes: 0a9fe8ca844d (x86/mm: Validate kernel_physical_mapping_init() ...)
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Tom Lendacky <Thomas.Lendacky@....com>
---
 arch/x86/mm/init_64.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index bccff68e3267..0a26b64a99b9 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -536,7 +536,7 @@ phys_pmd_init(pmd_t *pmd_page, unsigned long paddr, unsigned long paddr_end,
 		paddr_last = phys_pte_init(pte, paddr, paddr_end, new_prot);
 
 		spin_lock(&init_mm.page_table_lock);
-		pmd_populate_kernel_safe(&init_mm, pmd, pte);
+		pmd_populate_kernel(&init_mm, pmd, pte);
 		spin_unlock(&init_mm.page_table_lock);
 	}
 	update_page_count(PG_LEVEL_2M, pages);
@@ -623,7 +623,7 @@ phys_pud_init(pud_t *pud_page, unsigned long paddr, unsigned long paddr_end,
 					   page_size_mask, prot);
 
 		spin_lock(&init_mm.page_table_lock);
-		pud_populate_safe(&init_mm, pud, pmd);
+		pud_populate(&init_mm, pud, pmd);
 		spin_unlock(&init_mm.page_table_lock);
 	}
 
-- 
2.17.1