linux-kernel - [tip: x86/cc] x86/mm: Do not zap page table entries mapping unaccepted memory table during kdump

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Date: Tue, 18 Jun 2024 14:01:40 -0000
From: "tip-bot2 for Ashish Kalra" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Ashish Kalra <ashish.kalra@....com>,
 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 "Borislav Petkov (AMD)" <bp@...en8.de>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: x86/cc] x86/mm: Do not zap page table entries mapping
 unaccepted memory table during kdump

The following commit has been merged into the x86/cc branch of tip:

Commit-ID:     5574b368873d4f24e2ae8fab3a1105ede252e542
Gitweb:        https://git.kernel.org/tip/5574b368873d4f24e2ae8fab3a1105ede252e542
Author:        Ashish Kalra <ashish.kalra@....com>
AuthorDate:    Fri, 14 Jun 2024 12:58:58 +03:00
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Mon, 17 Jun 2024 17:46:12 +02:00

x86/mm: Do not zap page table entries mapping unaccepted memory table during kdump

During crashkernel boot only pre-allocated crash memory is presented as
E820_TYPE_RAM.

This can cause page table entries mapping unaccepted memory table to be zapped
during phys_pte_init(), phys_pmd_init(), phys_pud_init() and phys_p4d_init() as
SNP/TDX guest use E820_TYPE_ACPI to store the unaccepted memory table and pass
it between the kernels on kexec/kdump.

E820_TYPE_ACPI covers not only ACPI data, but also EFI tables and might be
required by kernel to function properly.

The problem was discovered during debugging kdump for SNP guest. The unaccepted
memory table stored with E820_TYPE_ACPI and passed between the kernels on kdump
was getting zapped as the PMD entry mapping this is above the E820_TYPE_RAM
range for the reserved crashkernel memory.

Signed-off-by: Ashish Kalra <ashish.kalra@....com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Link: https://lore.kernel.org/r/20240614095904.1345461-14-kirill.shutemov@linux.intel.com
---
 arch/x86/mm/init_64.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 7e17785..28002cc 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -469,7 +469,9 @@ phys_pte_init(pte_t *pte_page, unsigned long paddr, unsigned long paddr_end,
 			    !e820__mapped_any(paddr & PAGE_MASK, paddr_next,
 					     E820_TYPE_RAM) &&
 			    !e820__mapped_any(paddr & PAGE_MASK, paddr_next,
-					     E820_TYPE_RESERVED_KERN))
+					     E820_TYPE_RESERVED_KERN) &&
+			    !e820__mapped_any(paddr & PAGE_MASK, paddr_next,
+					     E820_TYPE_ACPI))
 				set_pte_init(pte, __pte(0), init);
 			continue;
 		}
@@ -524,7 +526,9 @@ phys_pmd_init(pmd_t *pmd_page, unsigned long paddr, unsigned long paddr_end,
 			    !e820__mapped_any(paddr & PMD_MASK, paddr_next,
 					     E820_TYPE_RAM) &&
 			    !e820__mapped_any(paddr & PMD_MASK, paddr_next,
-					     E820_TYPE_RESERVED_KERN))
+					     E820_TYPE_RESERVED_KERN) &&
+			    !e820__mapped_any(paddr & PMD_MASK, paddr_next,
+					     E820_TYPE_ACPI))
 				set_pmd_init(pmd, __pmd(0), init);
 			continue;
 		}
@@ -611,7 +615,9 @@ phys_pud_init(pud_t *pud_page, unsigned long paddr, unsigned long paddr_end,
 			    !e820__mapped_any(paddr & PUD_MASK, paddr_next,
 					     E820_TYPE_RAM) &&
 			    !e820__mapped_any(paddr & PUD_MASK, paddr_next,
-					     E820_TYPE_RESERVED_KERN))
+					     E820_TYPE_RESERVED_KERN) &&
+			    !e820__mapped_any(paddr & PUD_MASK, paddr_next,
+					     E820_TYPE_ACPI))
 				set_pud_init(pud, __pud(0), init);
 			continue;
 		}
@@ -698,7 +704,9 @@ phys_p4d_init(p4d_t *p4d_page, unsigned long paddr, unsigned long paddr_end,
 			    !e820__mapped_any(paddr & P4D_MASK, paddr_next,
 					     E820_TYPE_RAM) &&
 			    !e820__mapped_any(paddr & P4D_MASK, paddr_next,
-					     E820_TYPE_RESERVED_KERN))
+					     E820_TYPE_RESERVED_KERN) &&
+			    !e820__mapped_any(paddr & P4D_MASK, paddr_next,
+					     E820_TYPE_ACPI))
 				set_p4d_init(p4d, __p4d(0), init);
 			continue;
 		}