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SubjectRe: [PATCH 16/16] x86/entry/64: Move the IST stacks into cpu_entry_area
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On 11/21/2017 10:38 AM, Ingo Molnar wrote:
>
> * Andy Lutomirski <luto@kernel.org> wrote:
>
>> /* May not be marked __init: used by software suspend */
>> void syscall_init(void)
>> {
>> @@ -1627,7 +1637,7 @@ void cpu_init(void)
>> * set up and load the per-CPU TSS
>> */
>> if (!oist->ist[0]) {
>> - char *estacks = per_cpu(exception_stacks, cpu);
>> + char *estacks = get_cpu_entry_area(cpu)->exception_stacks;
>>
>> for (v = 0; v < N_EXCEPTION_STACKS; v++) {
>> estacks += exception_stack_sizes[v];
>
> This generates a new build warning:
>
> /home/mingo/tip/arch/x86/kernel/cpu/common.c: In function ‘syscall_init’:
> /home/mingo/tip/arch/x86/kernel/cpu/common.c:1443:6: warning: unused variable ‘cpu’ [-Wunused-variable]
> int cpu = smp_processor_id();
>
> because 'cpu' is now unused in the !CONFIG_IA32_EMULATION part.
>
> The naive fix is something like the patch below, untested.
>
> Thanks,
>
> Ingo
>
> arch/x86/kernel/cpu/common.c | 30 ++++++++++++++++--------------
> 1 file changed, 16 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index c7f3a0a19dce..557bad9f4179 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1440,24 +1440,26 @@ void syscall_init(void)
> extern char _entry_trampoline[];
> extern char entry_SYSCALL_64_trampoline[];
>
> - int cpu = smp_processor_id();
> -
> wrmsr(MSR_STAR, 0, (__USER32_CS << 16) | __KERNEL_CS);
> wrmsrl(MSR_LSTAR, (unsigned long)get_cpu_entry_area(smp_processor_id())->entry_trampoline + (entry_SYSCALL_64_trampoline - _entry_trampoline));

It would be better to use 'cpu' variable here ^^^^^^^^^^^^^^^^^
>
> #ifdef CONFIG_IA32_EMULATION
> - wrmsrl(MSR_CSTAR, (unsigned long)entry_SYSCALL_compat);
> - /*
> - * This only works on Intel CPUs.
> - * On AMD CPUs these MSRs are 32-bit, CPU truncates MSR_IA32_SYSENTER_EIP.
> - * This does not cause SYSENTER to jump to the wrong location, because
> - * AMD doesn't allow SYSENTER in long mode (either 32- or 64-bit).
> - */
> - wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)__KERNEL_CS);
> - wrmsrl_safe(MSR_IA32_SYSENTER_ESP,
> - (unsigned long)&get_cpu_entry_area(cpu)->tss +
> - offsetofend(struct tss_struct, SYSENTER_stack));
> - wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)entry_SYSENTER_compat);
> + {
> + int cpu = smp_processor_id();
> +
> + wrmsrl(MSR_CSTAR, (unsigned long)entry_SYSCALL_compat);
> + /*
> + * This only works on Intel CPUs.
> + * On AMD CPUs these MSRs are 32-bit, CPU truncates MSR_IA32_SYSENTER_EIP.
> + * This does not cause SYSENTER to jump to the wrong location, because
> + * AMD doesn't allow SYSENTER in long mode (either 32- or 64-bit).
> + */
> + wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)__KERNEL_CS);
> + wrmsrl_safe(MSR_IA32_SYSENTER_ESP,
> + (unsigned long)&get_cpu_entry_area(cpu)->tss +
> + offsetofend(struct tss_struct, SYSENTER_stack));
> + wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)entry_SYSENTER_compat);
> + }
> #else
> wrmsrl(MSR_CSTAR, (unsigned long)ignore_sysret);
> wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)GDT_ENTRY_INVALID_SEG);
>

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