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From: Ashish Kalra <Ashish.Kalra@amd.com>
To: <tglx@linutronix.de>, <mingo@redhat.com>, <dave.hansen@linux.intel.com>
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Subject: [PATCH v2 2/3] x86/mm: Do not zap page table entries mapping unaccepted memory table during kdump.
Date: Mon, 18 Mar 2024 07:02:45 +0000
Message-ID: <8e11825bb3e4a7472bf0cb30c72ae013c25ac8c9.1710744412.git.ashish.kalra@amd.com>
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From: Ashish Kalra <ashish.kalra@amd.com>

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@amd.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 a0dffaca6d2b..cc294a9e9fd7 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;
 		}
-- 
2.34.1