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x86: use MSRs for %gs

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We don't need to set up GDT data descriptors for setting
%gs. Instead, we use the x86 MSRs to set GS_BASE and
KERNEL_GS_BASE.

We don't currently allow user mode to set %gs on its own,
but later on if we do, we have everything set up to issue
'swapgs' instructions on syscall or IRQ.

Unused entries in the GDT have been removed.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
This commit is contained in:
Andrew Boie 2019-11-12 17:56:21 -08:00 • committed by Anas Nashif
commit 692fda47fc
5 changed files with 40 additions and 75 deletions
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8
arch/x86/core/intel64/cpu.c
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@ -65,7 +65,7 @@ extern struct x86_page_tables z_x86_flat_ptables;
struct x86_cpuboot x86_cpuboot[] = {
{
.tr = X86_KERNEL_CPU0_TR,
.gs = X86_KERNEL_CPU0_GS,
.gs_base = &tss0,
.sp = (u64_t) _interrupt_stack + CONFIG_ISR_STACK_SIZE,
.fn = z_x86_prep_c,
#ifdef CONFIG_X86_MMU
@ -75,19 +75,19 @@ struct x86_cpuboot x86_cpuboot[] = {
#if CONFIG_MP_NUM_CPUS > 1
{
.tr = X86_KERNEL_CPU1_TR,
.gs = X86_KERNEL_CPU1_GS,
.gs_base = &tss1
},
#endif
#if CONFIG_MP_NUM_CPUS > 2
{
.tr = X86_KERNEL_CPU2_TR,
.gs = X86_KERNEL_CPU2_GS,
.gs_base = &tss2
},
#endif
#if CONFIG_MP_NUM_CPUS > 3
{
.tr = X86_KERNEL_CPU3_TR,
.gs = X86_KERNEL_CPU3_GS,
.gs_base = &tss3
},
#endif
};