Aren
/
NetBSD
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Improve our segregs model. Pass 1/3. 

Right now, we are saving and restoring %ds/%es each time we enter/leave the
kernel. However, we let %fs/%gs live in the kernel space, and we rely on
the fact that when switching to an LWP, %fs/%gs are set right away (via
cpu_switchto or setregs).

It has two drawbacks: we are taking care of %ds/%es while they are
deprecated (useless) on 64bit LWPs, and we are restricting %fs/%gs while
they still have a meaning on 32bit LWPs.

Therefore, handle 32bit and 64bit LWPs differently:
 * 64bit LWPs use fixed segregs, which are not taken care of.
 * 32bit LWPs have dynamic segregs, always saved/restored.

For now, only %ds and %es are changed; %fs and %gs will be in the next
passes.

The trapframe is constructed as usual. In INTRFASTEXIT, we restore %ds/%es
depending on the %cs value. If %cs contains one of the two standard 64bit
selectors, don't do anything. Otherwise, restore everything.

When doing a context switch, just restore %ds/%es to their default values.
On a 32bit LWP they will be overwritten by INTRFASTEXIT; on a 64bit LWP
they won't be updated.

In the ACPI wakeup code, restore %ds/%es to the default 64bit user value.
This commit is contained in:
maxv 2017-10-19 18:36:31 +00:00
parent 9288b0c345
commit 5aa55d4fc6
3 changed files with 51 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
sys/arch/amd64/acpi/acpi_wakeup_low.S
View File

@ -1,4 +1,4 @@
/* $NetBSD: acpi_wakeup_low.S,v 1.6 2017/09/23 10:18:49 maxv Exp $ */
/* $NetBSD: acpi_wakeup_low.S,v 1.7 2017/10/19 18:36:31 maxv Exp $ */
/*-
* Copyright (c) 2007 Joerg Sonnenberger <joerg@netbsd.org>
@ -40,12 +40,17 @@ acpi_md_sleep_exit:
lgdt ACPI_SUSPEND_GDT(%r8)
/* Reload fixed descriptors for new GDT */
movw $GSEL(GDATA_SEL, SEL_KPL),%ax
movw $GSEL(GUDATA_SEL, SEL_UPL),%ax
movw %ax,%ds
movw %ax,%es
movw $GSEL(GDATA_SEL, SEL_KPL),%ax
movw %ax,%ss
/* FS and GS are driven by MSRs, so use NULL for them */
/*
* FS and GS are driven by MSRs, so use NULL for them.
* XXX XXX XXX That's not the case if we're returning to a 32bit
* LWP!
*/
xorw %ax,%ax
movw %ax,%fs
movw %ax,%gs

49
sys/arch/amd64/amd64/locore.S
View File

@ -1,4 +1,4 @@
/* $NetBSD: locore.S,v 1.133 2017/10/17 07:48:10 maxv Exp $ */
/* $NetBSD: locore.S,v 1.134 2017/10/19 18:36:31 maxv Exp $ */
/*
* Copyright-o-rama!
@ -1159,7 +1159,10 @@ skip_CR0:
jnz lwp_32bit
lwp_64bit:
/* Zero out %fs/%gs registers. */
/* Set default 64bit values in %ds, %es, %fs and %gs. */
movq $GSEL(GUDATA_SEL, SEL_UPL),%rax
movw %ax,%ds
movw %ax,%es
xorq %rax,%rax
movw %ax,%fs
CLI(cx)
@ -1193,8 +1196,11 @@ lwp_32bit:
movq PCB_GS(%r14),%rax
movq %rax,(GUGS_SEL*8)(%rcx)
/* Reload %fs and %gs */
/* Set default 32bit values in %ds, %es. %fs and %gs are special. */
movq L_MD_REGS(%r12),%rbx
movq $GSEL(GUDATA32_SEL, SEL_UPL),%rax
movw %ax,%ds
movw %ax,%es
movw TF_FS(%rbx),%fs
CLI(ax)
SWAPGS
@ -1281,10 +1287,10 @@ IDTVEC(syscall)
cld
#endif
INTR_SAVE_GPRS
movw %es,TF_ES(%rsp)
movw %fs,TF_FS(%rsp)
movw %gs,TF_GS(%rsp)
movw $(GSEL(GUDATA_SEL, SEL_UPL)),TF_DS(%rsp)
movw $GSEL(GUDATA_SEL, SEL_UPL),TF_DS(%rsp)
movw $GSEL(GUDATA_SEL, SEL_UPL),TF_ES(%rsp)
movw $0,TF_FS(%rsp)
movw $0,TF_GS(%rsp)
STI(si)
do_syscall:
@ -1313,18 +1319,18 @@ do_syscall:
#endif
/*
* If the syscall might have modified some registers, or we are a 32bit
* process we must return to user with an 'iret' instruction.
* If the iret faults in kernel (assumed due to illegal register values)
* then a SIGSEGV will be signalled.
* Decide if we need to take a slow path. That's the case when we
* want to reload %cs and %ss on a 64bit LWP (MDL_IRET set), or when
* we're returning to a 32bit LWP (MDL_COMPAT32 set).
*
* In either case, we jump into intrfastexit and return to userland
* with the iret instruction.
*/
testl $(MDL_IRET|MDL_COMPAT32),L_MD_FLAGS(%r14)
INTR_RESTORE_GPRS
movw TF_ES(%rsp),%es
movw TF_DS(%rsp),%ds
SWAPGS
jnz .Lkexit
jnz intrfastexit
INTR_RESTORE_GPRS
SWAPGS
#ifndef XEN
movq TF_RIP(%rsp),%rcx /* %rip for sysret */
movq TF_RFLAGS(%rsp),%r11 /* %flags for sysret */
@ -1469,12 +1475,21 @@ ENTRY(intrfastexit)
INTR_RESTORE_GPRS
testq $SEL_UPL,TF_CS(%rsp) /* interrupted %cs */
jz .Lkexit
cmpq $LSEL(LUCODE_SEL, SEL_UPL),TF_CS(%rsp)
je .Luexit64
cmpq $GSEL(GUCODE_SEL, SEL_UPL),TF_CS(%rsp)
je .Luexit64
/* Disable interrupts until the 'iret', user registers loaded. */
.Luexit32:
NOT_XEN(cli;)
movw TF_ES(%rsp),%es
movw TF_DS(%rsp),%ds
SWAPGS
jmp .Lkexit
.Luexit64:
NOT_XEN(cli;)
SWAPGS
.Lkexit:
addq $TF_REGSIZE+16,%rsp /* + T_xxx and error code */

14
sys/arch/amd64/amd64/machdep.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: machdep.c,v 1.269 2017/10/19 10:01:09 maxv Exp $ */
/* $NetBSD: machdep.c,v 1.270 2017/10/19 18:36:31 maxv Exp $ */
/*
* Copyright (c) 1996, 1997, 1998, 2000, 2006, 2007, 2008, 2011
@ -110,7 +110,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: machdep.c,v 1.269 2017/10/19 10:01:09 maxv Exp $");
__KERNEL_RCSID(0, "$NetBSD: machdep.c,v 1.270 2017/10/19 18:36:31 maxv Exp $");
/* #define XENDEBUG_LOW */
@ -447,15 +447,19 @@ x86_64_tls_switch(struct lwp *l)
HYPERVISOR_fpu_taskswitch(1);
}
/* Update TLS segment pointers */
/* Update segment registers */
if (pcb->pcb_flags & PCB_COMPAT32) {
update_descriptor(&curcpu()->ci_gdt[GUFS_SEL], &pcb->pcb_fs);
update_descriptor(&curcpu()->ci_gdt[GUGS_SEL], &pcb->pcb_gs);
setds(GSEL(GUDATA32_SEL, SEL_UPL));
setes(GSEL(GUDATA32_SEL, SEL_UPL));
setfs(tf->tf_fs);
HYPERVISOR_set_segment_base(SEGBASE_GS_USER_SEL, tf->tf_gs);
} else {
update_descriptor(&curcpu()->ci_gdt[GUFS_SEL], &zero);
update_descriptor(&curcpu()->ci_gdt[GUGS_SEL], &zero);
setds(GSEL(GUDATA_SEL, SEL_UPL));
setes(GSEL(GUDATA_SEL, SEL_UPL));
setfs(0);
HYPERVISOR_set_segment_base(SEGBASE_GS_USER_SEL, 0);
HYPERVISOR_set_segment_base(SEGBASE_FS, pcb->pcb_fs);
@ -2063,6 +2067,8 @@ cpu_segregs64_zero(struct lwp *l)
kpreempt_disable();
tf->tf_fs = 0;
tf->tf_gs = 0;
setds(GSEL(GUDATA_SEL, SEL_UPL));
setes(GSEL(GUDATA_SEL, SEL_UPL));
setfs(0);
setusergs(0);
@ -2100,6 +2106,8 @@ cpu_segregs32_zero(struct lwp *l)
kpreempt_disable();
tf->tf_fs = 0;
tf->tf_gs = 0;
setds(GSEL(GUDATA32_SEL, SEL_UPL));
setes(GSEL(GUDATA32_SEL, SEL_UPL));
setfs(0);
setusergs(0);
pcb->pcb_fs = 0;