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SubjectRe: [PATCH 02/16] x86/entry/32: Enter the kernel via trampoline stack
On Tue, Jan 16, 2018 at 12:30 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> On Tue, 16 Jan 2018, Joerg Roedel wrote:
>> @@ -89,13 +89,9 @@ static inline void refresh_sysenter_cs(struct thread_struct *thread)
>> /* This is used when switching tasks or entering/exiting vm86 mode. */
>> static inline void update_sp0(struct task_struct *task)
>> {
>> - /* On x86_64, sp0 always points to the entry trampoline stack, which is constant: */
>> -#ifdef CONFIG_X86_32
>> - load_sp0(task->thread.sp0);
>> -#else
>> + /* sp0 always points to the entry trampoline stack, which is constant: */
>> if (static_cpu_has(X86_FEATURE_XENPV))
>> load_sp0(task_top_of_stack(task));
>> -#endif
>> }
>>
>> #endif /* _ASM_X86_SWITCH_TO_H */
>> diff --git a/arch/x86/kernel/asm-offsets_32.c b/arch/x86/kernel/asm-offsets_32.c
>> index 654229bac2fc..7270dd834f4b 100644
>> --- a/arch/x86/kernel/asm-offsets_32.c
>> +++ b/arch/x86/kernel/asm-offsets_32.c
>> @@ -47,9 +47,11 @@ void foo(void)
>> BLANK();
>>
>> /* Offset from the sysenter stack to tss.sp0 */
>> - DEFINE(TSS_sysenter_stack, offsetof(struct cpu_entry_area, tss.x86_tss.sp0) -
>> + DEFINE(TSS_sysenter_stack, offsetof(struct cpu_entry_area, tss.x86_tss.sp1) -
>> offsetofend(struct cpu_entry_area, entry_stack_page.stack));

I was going to say that this is just too magical. The convention is
that STRUCT_member refers to "member" of "STRUCT". Here you're
encoding a more complicated calculation. How about putting just the
needed offsets in asm_offsets and putting the actual calculation in
the asm code or a header.

>>
>> + OFFSET(TSS_sp1, tss_struct, x86_tss.sp1);

This belongs in asm_offsets.c. Just move the asm_offsets_64.c version
there and call it a day.

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