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Kernel: Use the GS segment for the per-CPU struct

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Right now we're using the FS segment for our per-CPU struct. On x86_64
there's an instruction to switch between a kernel and usermode GS
segment (swapgs) which we could use.

This patch doesn't update the rest of the code to use swapgs but it
prepares for that by using the GS segment instead of the FS segment.
This commit is contained in:
Gunnar Beutner 2021-07-02 14:02:36 +02:00 • committed by Andreas Kling
parent 42d197cde7
commit 52f9aaa823
8 changed files with 36 additions and 36 deletions
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30
Kernel/Arch/x86/common/Processor.cpp
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@ -1092,17 +1092,17 @@ UNMAP_AFTER_INIT void Processor::gdt_init()
tls_descriptor.type = 2;
write_gdt_entry(GDT_SELECTOR_TLS, tls_descriptor); // tls3
Descriptor fs_descriptor {};
fs_descriptor.set_base(VirtualAddress { this });
fs_descriptor.set_limit(sizeof(Processor) - 1);
fs_descriptor.dpl = 0;
fs_descriptor.segment_present = 1;
fs_descriptor.granularity = 0;
fs_descriptor.operation_size64 = 0;
fs_descriptor.operation_size32 = 1;
fs_descriptor.descriptor_type = 1;
fs_descriptor.type = 2;
write_gdt_entry(GDT_SELECTOR_PROC, fs_descriptor); // fs0
Descriptor gs_descriptor {};
gs_descriptor.set_base(VirtualAddress { this });
gs_descriptor.set_limit(sizeof(Processor) - 1);
gs_descriptor.dpl = 0;
gs_descriptor.segment_present = 1;
gs_descriptor.granularity = 0;
gs_descriptor.operation_size64 = 0;
gs_descriptor.operation_size32 = 1;
gs_descriptor.descriptor_type = 1;
gs_descriptor.type = 2;
write_gdt_entry(GDT_SELECTOR_PROC, gs_descriptor); // gs0
#endif
Descriptor tss_descriptor {};
@ -1127,16 +1127,16 @@ UNMAP_AFTER_INIT void Processor::gdt_init()
load_task_register(GDT_SELECTOR_TSS);
#if ARCH(X86_64)
MSR fs_base(MSR_FS_BASE);
fs_base.set((size_t)this & 0xffffffff, (size_t)this >> 32);
MSR gs_base(MSR_GS_BASE);
gs_base.set((size_t)this & 0xffffffff, (size_t)this >> 32);
#else
asm volatile(
"mov %%ax, %%ds\n"
"mov %%ax, %%es\n"
"mov %%ax, %%gs\n"
"mov %%ax, %%fs\n"
"mov %%ax, %%ss\n" ::"a"(GDT_SELECTOR_DATA0)
: "memory");
set_fs(GDT_SELECTOR_PROC);
set_gs(GDT_SELECTOR_PROC);
#endif
#if ARCH(I386)