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x86/asm: Add DB flag to 32-bit percpu GDT entry 

The D/B size flag for the 32-bit percpu GDT entry was not set.

The Intel manual (vol 3, section 3.4.5) only specifies the meaning of
this flag for three cases:

 1) code segments used for %cs -- doesn't apply here

 2) stack segments used for %ss -- doesn't apply

 3) expand-down data segments -- but we don't have the expand-down flag
    set, so it also doesn't apply here

The flag likely doesn't do anything here, although the manual does also
say: "This flag should always be set to 1 for 32-bit code and data
segments [...]" so we should probably do it anyway.

Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20231219151200.2878271-6-vegard.nossum@oracle.com
This commit is contained in:
Vegard Nossum 2023-12-19 16:12:00 +01:00 committed by Ingo Molnar
parent 3b184b71df
commit bc90aefa99
1 changed files with 1 additions and 1 deletions
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2
arch/x86/kernel/setup_percpu.c
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@ -106,7 +106,7 @@ void __init pcpu_populate_pte(unsigned long addr)
static inline void setup_percpu_segment(int cpu)
{
#ifdef CONFIG_X86_32
struct desc_struct d = GDT_ENTRY_INIT(DESC_DATA32 & ~_DESC_DB,
struct desc_struct d = GDT_ENTRY_INIT(DESC_DATA32,
per_cpu_offset(cpu), 0xFFFFF);
write_gdt_entry(get_cpu_gdt_rw(cpu), GDT_ENTRY_PERCPU, &d, DESCTYPE_S);