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SubjectRe: [PATCH 16/16] x86/entry/64: Move the IST stacks into cpu_entry_area

* 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));

#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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