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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-12-11 17:36:49 +07:00
e9f86e351f
When reviewing GDT updates, I found the code:
set_tss_desc(cpu,t); /* This just modifies memory; ... */
per_cpu(cpu_gdt_table, cpu)[GDT_ENTRY_TSS].b &= 0xfffffdff;
This second line is unnecessary, since set_tss_desc() has already cleared
the busy bit.
Commented disassembly, line 1:
c028b8bd: 8b 0c 86 mov (%esi,%eax,4),%ecx
c028b8c0: 01 cb add %ecx,%ebx
c028b8c2: 8d 0c 39 lea (%ecx,%edi,1),%ecx
=> %ecx = per_cpu(cpu_gdt_table, cpu)
c028b8c5: 8d 91 80 00 00 00 lea 0x80(%ecx),%edx
=> %edx = &per_cpu(cpu_gdt_table, cpu)[GDT_ENTRY_TSS]
c028b8cb: 66 c7 42 00 73 20 movw $0x2073,0x0(%edx)
c028b8d1: 66 89 5a 02 mov %bx,0x2(%edx)
c028b8d5: c1 cb 10 ror $0x10,%ebx
c028b8d8: 88 5a 04 mov %bl,0x4(%edx)
c028b8db: c6 42 05 89 movb $0x89,0x5(%edx)
=> ((char *)%edx)[5] = 0x89
(equivalent) ((char *)per_cpu(cpu_gdt_table, cpu)[GDT_ENTRY_TSS])[5] = 0x89
c028b8df: c6 42 06 00 movb $0x0,0x6(%edx)
c028b8e3: 88 7a 07 mov %bh,0x7(%edx)
c028b8e6: c1 cb 10 ror $0x10,%ebx
=> other bits
Commented disassembly, line 2:
c028b8e9: 8b 14 86 mov (%esi,%eax,4),%edx
c028b8ec: 8d 04 3a lea (%edx,%edi,1),%eax
=> %eax = per_cpu(cpu_gdt_table, cpu)
c028b8ef: 81 a0 84 00 00 00 ff andl $0xfffffdff,0x84(%eax)
=> per_cpu(cpu_gdt_table, cpu)[GDT_ENTRY_TSS].b &= 0xfffffdff;
(equivalent) ((char *)per_cpu(cpu_gdt_table, cpu)[GDT_ENTRY_TSS])[5] &= 0xfd
Note that (0x89 & ~0xfd) == 0; i.e, set_tss_desc(cpu,t) has already stored
the type field in the GDT with the busy bit clear.
Eliminating redundant and obscure code is always a good thing; in fact, I
pointed out this same optimization many moons ago in arch/i386/setup.c,
back when it used to be called that.
Signed-off-by: Zachary Amsden <zach@vmware.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
150 lines
3.2 KiB
C
150 lines
3.2 KiB
C
/*
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* Suspend support specific for i386.
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*
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* Distribute under GPLv2
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*
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* Copyright (c) 2002 Pavel Machek <pavel@suse.cz>
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* Copyright (c) 2001 Patrick Mochel <mochel@osdl.org>
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*/
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#include <linux/config.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/types.h>
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#include <linux/spinlock.h>
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#include <linux/poll.h>
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#include <linux/delay.h>
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#include <linux/sysrq.h>
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#include <linux/proc_fs.h>
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#include <linux/irq.h>
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#include <linux/pm.h>
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#include <linux/device.h>
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#include <linux/suspend.h>
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#include <linux/acpi.h>
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#include <asm/uaccess.h>
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#include <asm/acpi.h>
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#include <asm/tlbflush.h>
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#include <asm/processor.h>
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static struct saved_context saved_context;
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unsigned long saved_context_ebx;
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unsigned long saved_context_esp, saved_context_ebp;
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unsigned long saved_context_esi, saved_context_edi;
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unsigned long saved_context_eflags;
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void __save_processor_state(struct saved_context *ctxt)
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{
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kernel_fpu_begin();
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/*
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* descriptor tables
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*/
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store_gdt(&ctxt->gdt_limit);
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store_idt(&ctxt->idt_limit);
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store_tr(ctxt->tr);
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/*
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* segment registers
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*/
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savesegment(es, ctxt->es);
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savesegment(fs, ctxt->fs);
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savesegment(gs, ctxt->gs);
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savesegment(ss, ctxt->ss);
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/*
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* control registers
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*/
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ctxt->cr0 = read_cr0();
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ctxt->cr2 = read_cr2();
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ctxt->cr3 = read_cr3();
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ctxt->cr4 = read_cr4();
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}
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void save_processor_state(void)
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{
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__save_processor_state(&saved_context);
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}
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static void
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do_fpu_end(void)
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{
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/* restore FPU regs if necessary */
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/* Do it out of line so that gcc does not move cr0 load to some stupid place */
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kernel_fpu_end();
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mxcsr_feature_mask_init();
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}
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static void fix_processor_context(void)
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{
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int cpu = smp_processor_id();
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struct tss_struct * t = &per_cpu(init_tss, cpu);
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set_tss_desc(cpu,t); /* This just modifies memory; should not be necessary. But... This is necessary, because 386 hardware has concept of busy TSS or some similar stupidity. */
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load_TR_desc(); /* This does ltr */
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load_LDT(¤t->active_mm->context); /* This does lldt */
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/*
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* Now maybe reload the debug registers
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*/
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if (current->thread.debugreg[7]){
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set_debugreg(current->thread.debugreg[0], 0);
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set_debugreg(current->thread.debugreg[1], 1);
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set_debugreg(current->thread.debugreg[2], 2);
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set_debugreg(current->thread.debugreg[3], 3);
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/* no 4 and 5 */
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set_debugreg(current->thread.debugreg[6], 6);
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set_debugreg(current->thread.debugreg[7], 7);
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}
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}
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void __restore_processor_state(struct saved_context *ctxt)
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{
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/*
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* control registers
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*/
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write_cr4(ctxt->cr4);
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write_cr3(ctxt->cr3);
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write_cr2(ctxt->cr2);
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write_cr2(ctxt->cr0);
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/*
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* now restore the descriptor tables to their proper values
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* ltr is done i fix_processor_context().
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*/
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load_gdt(&ctxt->gdt_limit);
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load_idt(&ctxt->idt_limit);
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/*
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* segment registers
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*/
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loadsegment(es, ctxt->es);
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loadsegment(fs, ctxt->fs);
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loadsegment(gs, ctxt->gs);
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loadsegment(ss, ctxt->ss);
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/*
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* sysenter MSRs
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*/
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if (boot_cpu_has(X86_FEATURE_SEP))
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enable_sep_cpu();
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fix_processor_context();
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do_fpu_end();
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mtrr_ap_init();
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}
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void restore_processor_state(void)
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{
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__restore_processor_state(&saved_context);
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}
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/* Needed by apm.c */
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EXPORT_SYMBOL(save_processor_state);
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EXPORT_SYMBOL(restore_processor_state);
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