Attachment 303656 Details for Bug 442949 – clear %fs when loading new TLS descriptors (1/2)

[patch] clear %fs when loading new TLS descriptors (1/2)

fs-descriptor-clear-1.patch (text/plain), 1.96 KB, created by Eduardo Habkost on 2008-04-24 16:09:39 UTC

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Creator: Eduardo Habkost

Created: 2008-04-24 16:09:39 UTC

Size: 1.96 KB

patch

obsolete

>commit 060080092626758fab58986eb2c0563c30fb1416
>Author: Eduardo Habkost <ehabkost@redhat.com>
>Date:   Mon Apr 7 15:40:43 2008 -0300
>
>    Save %fs and %gs before load_TLS() and arch_leave_lazy_cpu_mode()
>    
>    We must do this because load_TLS() may need to clear %fs and %gs,
>    such (e.g. under Xen).
>    
>    Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
>
>diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
>index cf9ff51..d3fba53 100644
>--- a/arch/x86/kernel/process_64.c
>+++ b/arch/x86/kernel/process_64.c
>@@ -604,6 +604,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
> 				 *next = &next_p->thread;
> 	int cpu = smp_processor_id();
> 	struct tss_struct *tss = &per_cpu(init_tss, cpu);
>+	unsigned fsindex, gsindex;
> 
> 	/* we're going to use this soon, after a few expensive things */
> 	if (next_p->fpu_counter>5)
>@@ -626,6 +627,15 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
> 	if (unlikely(next->ds | prev->ds))
> 		loadsegment(ds, next->ds);
> 
>+
>+	/* We must save %fs and %gs before load_TLS() because
>+	 * %fs and %gs may be cleared by load_TLS().
>+	 *
>+	 * (e.g. xen_load_tls())
>+	 */
>+	asm volatile("movl %%fs,%0" : "=r" (fsindex)); 
>+	asm volatile("movl %%gs,%0" : "=r" (gsindex)); 
>+
> 	load_TLS(next, cpu);
> 
> 	/*
>@@ -641,8 +651,6 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
> 	 * Switch FS and GS.
> 	 */
> 	{ 
>-		unsigned fsindex;
>-		asm volatile("movl %%fs,%0" : "=r" (fsindex)); 
> 		/* segment register != 0 always requires a reload. 
> 		   also reload when it has changed. 
> 		   when prev process used 64bit base always reload
>@@ -660,10 +668,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
> 		if (next->fs) 
> 			wrmsrl(MSR_FS_BASE, next->fs); 
> 		prev->fsindex = fsindex;
>-	}
>-	{ 
>-		unsigned gsindex;
>-		asm volatile("movl %%gs,%0" : "=r" (gsindex)); 
>+
> 		if (unlikely(gsindex | next->gsindex | prev->gs)) {
> 			load_gs_index(next->gsindex);
> 			if (gsindex)

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Attachments on bug 442949: 302798 | 303656 | 303657