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Date:      Tue, 30 Apr 2013 05:39:43 +0000 (UTC)
From:      "Cherry G. Mathew" <cherry@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-projects@freebsd.org
Subject:   svn commit: r250091 - projects/amd64_xen_pv/sys/amd64/xen
Message-ID:  <201304300539.r3U5dhtP073451@svn.freebsd.org>
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Author: cherry
Date: Tue Apr 30 05:39:42 2013
New Revision: 250091
URL: http://svnweb.freebsd.org/changeset/base/250091

Log:
  On Xen, %fs and %gs are set via hypercalls.
  We thus set the %fs and %gs selectors to 0
  and ignore trapframe values on return to userspace.
  Userspace sets %fs via sysarch(2), and the kernel dtrt.
  
  Approved by: gibbs (implicit)

Modified:
  projects/amd64_xen_pv/sys/amd64/xen/exception.S
  projects/amd64_xen_pv/sys/amd64/xen/machdep.c

Modified: projects/amd64_xen_pv/sys/amd64/xen/exception.S
==============================================================================
--- projects/amd64_xen_pv/sys/amd64/xen/exception.S	Tue Apr 30 05:32:07 2013	(r250090)
+++ projects/amd64_xen_pv/sys/amd64/xen/exception.S	Tue Apr 30 05:39:42 2013	(r250091)
@@ -100,7 +100,8 @@
 /* Save generic data segment registers to the stack */	
 #define SAVE_SEGMENT_REGS \
 	movw	%es, TF_ES(%rsp) ; \
-	movw	%ds, TF_DS(%rsp)
+	movw	%ds, TF_DS(%rsp) ; \
+	movw	%fs, TF_FS(%rsp)
 
 /* Restore generic data segment registers from the stack */
 #define RESTORE_SEGMENT_REGS \
@@ -118,7 +119,7 @@
  * [DS-GS,] is only saved for the failsafe callback.
  *
  * [ERRCODE], is optional, depending on the type of (hardware) exception.
- *  See: the "AMD64 Architecture Programmer's Manuel, Volume 2:
+ *  See: the "AMD64 Architecture Programmer's Manual, Volume 2:
  *  System Programming: Section 8.2 for individual error code
  *  reporting status
  *
@@ -241,8 +242,8 @@ ld_es:
 	movw	(TF_ES + 8)(%rsp,1), %es ; /* Save on previous frame */
 ld_ds:
 	movw	(TF_DS + 8)(%rsp,1), %ds ; /* Save on previous frame */
-ld_fs:
-ld_gs:
+ld_fs:  /* %fs == 0 and the per-proc base is updated via xen_set_proc() */
+ld_gs: 	/* XEN manages %gs (swapgs) */
 	ret
 	
 	/* The path below should not have been reached. */

Modified: projects/amd64_xen_pv/sys/amd64/xen/machdep.c
==============================================================================
--- projects/amd64_xen_pv/sys/amd64/xen/machdep.c	Tue Apr 30 05:32:07 2013	(r250090)
+++ projects/amd64_xen_pv/sys/amd64/xen/machdep.c	Tue Apr 30 05:39:42 2013	(r250091)
@@ -413,7 +413,7 @@ initxen(struct start_info *si)
 	memset(dump_avail, 0 , sizeof dump_avail);
 
 	/* 
-	 * Setup kernel tls registers. pcpu needs them, and other
+	 * Setup kernel PCPU base. pcpu needs them, and other
 	 * parts of the early startup path use pcpu variables before
 	 * we have loaded the new Global Descriptor Table.
 	 */
@@ -514,9 +514,7 @@ initxen(struct start_info *si)
 	 * Refresh kernel tls registers since we've blown them away
 	 * via new GDT load. pcpu needs them.
 	 */
-	HYPERVISOR_set_segment_base (SEGBASE_FS, 0);
 	HYPERVISOR_set_segment_base (SEGBASE_GS_KERNEL, (uint64_t) pc);
-	HYPERVISOR_set_segment_base (SEGBASE_GS_USER, (uint64_t) 0);
 
 	/* per cpu structures for cpu0 */
 	pcpu_init(pc, 0, sizeof(struct pcpu));
@@ -596,7 +594,10 @@ initxen(struct start_info *si)
 	/* Load thread0 context */
 	load_ds(_udatasel);
 	load_es(_udatasel);
-	load_fs(_ufssel);
+	load_fs(0); /* reset %fs to 0 before 64bit base load */
+	HYPERVISOR_set_segment_base (SEGBASE_FS, 0);
+	HYPERVISOR_set_segment_base (SEGBASE_GS_USER_SEL, (uint64_t) 0);
+	HYPERVISOR_set_segment_base (SEGBASE_GS_USER, (uint64_t) 0);
 
 	/* setup proc 0's pcb */
 	thread0.td_pcb->pcb_flags = 0;
@@ -1378,15 +1379,13 @@ xen_set_proc(struct pcb *newpcb)
 				USD_SETBASE(&gsd, newpcb->pcb_fsbase);
 				xen_set_descriptor((vm_paddr_t)PCPU_GET(fs32p), (void *)&gsd);
 			}
-
 		} else {
-
 			HYPERVISOR_set_segment_base(SEGBASE_GS_USER_SEL, 
-						    _ugssel);
-			HYPERVISOR_set_segment_base(SEGBASE_FS,
-						    newpcb->pcb_fsbase);
+						    0);
 			HYPERVISOR_set_segment_base(SEGBASE_GS_USER, 
 						    newpcb->pcb_gsbase);
+			HYPERVISOR_set_segment_base(SEGBASE_FS,
+						    newpcb->pcb_fsbase);
 		}
 	}
 }

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