linux-kernel - [tip: x86/cc] x86/mm: Make e820__end_ram_pfn() cover E820_TYPE

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Message-ID: <171871930040.10875.17107246519344852310.tip-bot2@tip-bot2>
Date: Tue, 18 Jun 2024 14:01:40 -0000
From: "tip-bot2 for Kirill A. Shutemov" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 "Borislav Petkov (AMD)" <bp@...en8.de>, Dave Hansen <dave.hansen@...el.com>,
 Tao Liu <ltao@...hat.com>, x86@...nel.org, linux-kernel@...r.kernel.org
Subject:
 [tip: x86/cc] x86/mm: Make e820__end_ram_pfn() cover E820_TYPE_ACPI ranges

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

Commit-ID:     06fa48d85b09b3e67afeda220bc19f7102b53beb
Gitweb:        https://git.kernel.org/tip/06fa48d85b09b3e67afeda220bc19f7102b53beb
Author:        Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
AuthorDate:    Fri, 14 Jun 2024 12:58:57 +03:00
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Mon, 17 Jun 2024 17:46:08 +02:00

x86/mm: Make e820__end_ram_pfn() cover E820_TYPE_ACPI ranges

e820__end_of_ram_pfn() is used to calculate max_pfn which, among other things,
guides where direct mapping ends. Any memory above max_pfn is not going to be
present in the direct mapping.

e820__end_of_ram_pfn() finds the end of the RAM based on the highest
E820_TYPE_RAM range. But it doesn't includes E820_TYPE_ACPI ranges into
calculation.

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

Usually the problem is hidden because there is some E820_TYPE_RAM memory above
E820_TYPE_ACPI. But crashkernel only presents pre-allocated crash memory as
E820_TYPE_RAM on boot. If the pre-allocated range is small, it can fit under the
last E820_TYPE_ACPI range.

Modify e820__end_of_ram_pfn() and e820__end_of_low_ram_pfn() to cover
E820_TYPE_ACPI memory.

The problem was discovered during debugging kexec for TDX guest. TDX guest uses
E820_TYPE_ACPI to store the unaccepted memory bitmap and pass it between the
kernels on kexec.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Reviewed-by: Dave Hansen <dave.hansen@...el.com>
Tested-by: Tao Liu <ltao@...hat.com>
Link: https://lore.kernel.org/r/20240614095904.1345461-13-kirill.shutemov@linux.intel.com
---
 arch/x86/kernel/e820.c |  9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 68b09f7..4893d30 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -828,7 +828,7 @@ u64 __init e820__memblock_alloc_reserved(u64 size, u64 align)
 /*
  * Find the highest page frame number we have available
  */
-static unsigned long __init e820_end_pfn(unsigned long limit_pfn, enum e820_type type)
+static unsigned long __init e820__end_ram_pfn(unsigned long limit_pfn)
 {
 	int i;
 	unsigned long last_pfn = 0;
@@ -839,7 +839,8 @@ static unsigned long __init e820_end_pfn(unsigned long limit_pfn, enum e820_type
 		unsigned long start_pfn;
 		unsigned long end_pfn;

-		if (entry->type != type)
+		if (entry->type != E820_TYPE_RAM &&
+		    entry->type != E820_TYPE_ACPI)
 			continue;

 		start_pfn = entry->addr >> PAGE_SHIFT;
@@ -865,12 +866,12 @@ static unsigned long __init e820_end_pfn(unsigned long limit_pfn, enum e820_type

 unsigned long __init e820__end_of_ram_pfn(void)
 {
-	return e820_end_pfn(MAX_ARCH_PFN, E820_TYPE_RAM);
+	return e820__end_ram_pfn(MAX_ARCH_PFN);
 }

 unsigned long __init e820__end_of_low_ram_pfn(void)
 {
-	return e820_end_pfn(1UL << (32 - PAGE_SHIFT), E820_TYPE_RAM);
+	return e820__end_ram_pfn(1UL << (32 - PAGE_SHIFT));
 }

 static void __init early_panic(char *msg)