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Commit ada85708 authored by Jeremy Fitzhardinge's avatar Jeremy Fitzhardinge Committed by Ingo Molnar
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x86: remove open-coded save/load segment operations 



This removes a pile of buggy open-coded implementations of savesegment
and loadsegment.

(They are buggy because they don't have memory barriers to prevent
them from being reordered with respect to memory accesses.)

Signed-off-by: default avatarJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: xen-devel <xen-devel@lists.xensource.com>
Cc: Stephen Tweedie <sct@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent af2b1c60

arch/x86/kernel/cpu/common_64.c

+2 −1
Original line number Original line Diff line number Diff line
@@ -480,7 +480,8 @@ void pda_init(int cpu) 
	struct x8664_pda *pda = cpu_pda(cpu);

	struct x8664_pda *pda = cpu_pda(cpu);





	/* Setup up data that may be needed in __get_free_pages early */

	/* Setup up data that may be needed in __get_free_pages early */

	asm volatile("movl %0,%%fs ; movl %0,%%gs" :: "r" (0));

	loadsegment(fs, 0);

	loadsegment(gs, 0);

	/* Memory clobbers used to order PDA accessed */

	/* Memory clobbers used to order PDA accessed */

	mb();

	mb();

	wrmsrl(MSR_GS_BASE, pda);

	wrmsrl(MSR_GS_BASE, pda);

arch/x86/kernel/process_64.c

+15 −13
Original line number Original line Diff line number Diff line
@@ -335,10 +335,10 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long sp, 
	p->thread.fs = me->thread.fs;

	p->thread.fs = me->thread.fs;

	p->thread.gs = me->thread.gs;

	p->thread.gs = me->thread.gs;





	asm("mov %%gs,%0" : "=m" (p->thread.gsindex));

	savesegment(gs, p->thread.gsindex);

	asm("mov %%fs,%0" : "=m" (p->thread.fsindex));

	savesegment(fs, p->thread.fsindex);

	asm("mov %%es,%0" : "=m" (p->thread.es));

	savesegment(es, p->thread.es);

	asm("mov %%ds,%0" : "=m" (p->thread.ds));

	savesegment(ds, p->thread.ds);





	if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) {

	if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) {

		p->thread.io_bitmap_ptr = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);

		p->thread.io_bitmap_ptr = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
@@ -377,7 +377,9 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long sp, 
void

void

start_thread(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp)

start_thread(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp)

{

{

	asm volatile("movl %0, %%fs; movl %0, %%es; movl %0, %%ds" :: "r"(0));

	loadsegment(fs, 0);

	loadsegment(es, 0);

	loadsegment(ds, 0);

	load_gs_index(0);

	load_gs_index(0);

	regs->ip		= new_ip;

	regs->ip		= new_ip;

	regs->sp		= new_sp;

	regs->sp		= new_sp;
@@ -550,11 +552,11 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) 
	 * Switch DS and ES.

	 * Switch DS and ES.

	 * This won't pick up thread selector changes, but I guess that is ok.

	 * This won't pick up thread selector changes, but I guess that is ok.

	 */

	 */

	asm volatile("mov %%es,%0" : "=m" (prev->es));

	savesegment(es, prev->es);

	if (unlikely(next->es | prev->es))

	if (unlikely(next->es | prev->es))

		loadsegment(es, next->es); 

		loadsegment(es, next->es); 





	asm volatile ("mov %%ds,%0" : "=m" (prev->ds));

	savesegment(ds, prev->ds);

	if (unlikely(next->ds | prev->ds))

	if (unlikely(next->ds | prev->ds))

		loadsegment(ds, next->ds);

		loadsegment(ds, next->ds);
@@ -565,7 +567,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) 
	 */

	 */

	{ 

	{ 

		unsigned fsindex;

		unsigned fsindex;

		asm volatile("movl %%fs,%0" : "=r" (fsindex)); 

		savesegment(fs, fsindex);

		/* segment register != 0 always requires a reload. 

		/* segment register != 0 always requires a reload. 

		   also reload when it has changed. 

		   also reload when it has changed. 

		   when prev process used 64bit base always reload

		   when prev process used 64bit base always reload
@@ -586,7 +588,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) 
	}

	}

	{ 

	{ 

		unsigned gsindex;

		unsigned gsindex;

		asm volatile("movl %%gs,%0" : "=r" (gsindex)); 

		savesegment(gs, gsindex);

		if (unlikely(gsindex | next->gsindex | prev->gs)) {

		if (unlikely(gsindex | next->gsindex | prev->gs)) {

			load_gs_index(next->gsindex);

			load_gs_index(next->gsindex);

			if (gsindex)

			if (gsindex)
@@ -767,7 +769,7 @@ long do_arch_prctl(struct task_struct *task, int code, unsigned long addr) 
			set_32bit_tls(task, FS_TLS, addr);

			set_32bit_tls(task, FS_TLS, addr);

			if (doit) {

			if (doit) {

				load_TLS(&task->thread, cpu);

				load_TLS(&task->thread, cpu);

				asm volatile("movl %0,%%fs" :: "r"(FS_TLS_SEL));

				loadsegment(fs, FS_TLS_SEL);

			}

			}

			task->thread.fsindex = FS_TLS_SEL;

			task->thread.fsindex = FS_TLS_SEL;

			task->thread.fs = 0;

			task->thread.fs = 0;
@@ -777,7 +779,7 @@ long do_arch_prctl(struct task_struct *task, int code, unsigned long addr) 
			if (doit) {

			if (doit) {

				/* set the selector to 0 to not confuse

				/* set the selector to 0 to not confuse

				   __switch_to */

				   __switch_to */

				asm volatile("movl %0,%%fs" :: "r" (0));

				loadsegment(fs, 0);

				ret = checking_wrmsrl(MSR_FS_BASE, addr);

				ret = checking_wrmsrl(MSR_FS_BASE, addr);

			}

			}

		}

		}
@@ -800,7 +802,7 @@ long do_arch_prctl(struct task_struct *task, int code, unsigned long addr) 
		if (task->thread.gsindex == GS_TLS_SEL)

		if (task->thread.gsindex == GS_TLS_SEL)

			base = read_32bit_tls(task, GS_TLS);

			base = read_32bit_tls(task, GS_TLS);

		else if (doit) {

		else if (doit) {

			asm("movl %%gs,%0" : "=r" (gsindex));

			savesegment(gs, gsindex);

			if (gsindex)

			if (gsindex)

				rdmsrl(MSR_KERNEL_GS_BASE, base);

				rdmsrl(MSR_KERNEL_GS_BASE, base);

			else

			else