* [Xen-devel] [PATCH] x86/boot: Further minor GDT corrections
2019-08-19 13:42 [Xen-devel] [PATCH] x86/boot: Various bits of trampoline cleanup Andrew Cooper
@ 2019-08-19 13:42 ` Andrew Cooper
2019-08-27 14:49 ` Jan Beulich
2019-08-19 13:42 ` [Xen-devel] [PATCH] x86/boot: Reposition trampoline data Andrew Cooper
2019-08-19 13:42 ` [Xen-devel] [PATCH] x86/boot: Drop all use of lmsw Andrew Cooper
2 siblings, 1 reply; 8+ messages in thread
From: Andrew Cooper @ 2019-08-19 13:42 UTC (permalink / raw)
To: Xen-devel; +Cc: Andrew Cooper, Wei Liu, Jan Beulich, Roger Pau Monné
gdt_boot_descr and gdt_48 disagree on how long trampoline_gdt is.
Introduce an end label and have the linker calculate the size, rather than
hard coding it.
Also, just as with c/s af292b41e9, there is no point forcing the CPU to set
Access bits. Fix all remaining GDTs in Xen.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wl@xen.org>
CC: Roger Pau Monné <roger.pau@citrix.com>
The trampoline GDT access bits were actually noticed when trying to clean up
our boot time pagetables and map the trampoline read-only.
---
xen/arch/x86/boot/head.S | 2 +-
xen/arch/x86/boot/trampoline.S | 15 ++++++++-------
xen/arch/x86/x86_64/kexec_reloc.S | 4 ++--
3 files changed, 11 insertions(+), 10 deletions(-)
diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
index 26b680521d..9fdb9b3954 100644
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -129,7 +129,7 @@ multiboot2_header:
.word 0
gdt_boot_descr:
- .word 7*8-1
+ .word .Ltramopline_gdt_end - trampoline_gdt - 1
gdt_boot_base:
.long sym_offs(trampoline_gdt)
.long 0 /* Needed for 64-bit lgdt */
diff --git a/xen/arch/x86/boot/trampoline.S b/xen/arch/x86/boot/trampoline.S
index 7c6a2328d2..1761fc1213 100644
--- a/xen/arch/x86/boot/trampoline.S
+++ b/xen/arch/x86/boot/trampoline.S
@@ -63,22 +63,23 @@ trampoline_gdt:
/* 0x0000: unused */
.quad 0x0000000000000000
/* 0x0008: ring 0 code, 32-bit mode */
- .quad 0x00cf9a000000ffff
+ .quad 0x00cf9b000000ffff
/* 0x0010: ring 0 code, 64-bit mode */
- .quad 0x00af9a000000ffff
+ .quad 0x00af9b000000ffff
/* 0x0018: ring 0 data */
- .quad 0x00cf92000000ffff
+ .quad 0x00cf93000000ffff
/* 0x0020: real-mode code @ BOOT_TRAMPOLINE */
.long 0x0000ffff
- .long 0x00009a00
+ .long 0x00009b00
/* 0x0028: real-mode data @ BOOT_TRAMPOLINE */
.long 0x0000ffff
- .long 0x00009200
+ .long 0x00009300
/*
* 0x0030: ring 0 Xen data, 16 MiB size, base
* address is computed at runtime.
*/
- .quad 0x00c0920000000fff
+ .quad 0x00c0930000000fff
+.Ltramopline_gdt_end:
.pushsection .trampoline_rel, "a"
.long trampoline_gdt + BOOT_PSEUDORM_CS + 2 - .
@@ -182,7 +183,7 @@ start64:
.word 0
idt_48: .word 0, 0, 0 # base = limit = 0
.word 0
-gdt_48: .word 6*8-1
+gdt_48: .word .Ltramopline_gdt_end - trampoline_gdt - 1
.long bootsym_rel(trampoline_gdt,4)
/* The first page of trampoline is permanent, the rest boot-time only. */
diff --git a/xen/arch/x86/x86_64/kexec_reloc.S b/xen/arch/x86/x86_64/kexec_reloc.S
index 5bf61d5c2d..9e5b7a6ba1 100644
--- a/xen/arch/x86/x86_64/kexec_reloc.S
+++ b/xen/arch/x86/x86_64/kexec_reloc.S
@@ -182,8 +182,8 @@ compat_mode_gdt_desc:
.align 8
compat_mode_gdt:
.quad 0x0000000000000000 /* null */
- .quad 0x00cf92000000ffff /* 0x0008 ring 0 data */
- .quad 0x00cf9a000000ffff /* 0x0010 ring 0 code, compatibility */
+ .quad 0x00cf93000000ffff /* 0x0008 ring 0 data */
+ .quad 0x00cf9b000000ffff /* 0x0010 ring 0 code, compatibility */
compat_mode_idt:
.word 0 /* limit */
--
2.11.0
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^ permalink raw reply related [flat|nested] 8+ messages in thread* Re: [Xen-devel] [PATCH] x86/boot: Further minor GDT corrections
2019-08-19 13:42 ` [Xen-devel] [PATCH] x86/boot: Further minor GDT corrections Andrew Cooper
@ 2019-08-27 14:49 ` Jan Beulich
0 siblings, 0 replies; 8+ messages in thread
From: Jan Beulich @ 2019-08-27 14:49 UTC (permalink / raw)
To: Andrew Cooper; +Cc: Xen-devel, Wei Liu, Roger Pau Monné
On 19.08.2019 15:42, Andrew Cooper wrote:
> gdt_boot_descr and gdt_48 disagree on how long trampoline_gdt is.
>
> Introduce an end label and have the linker calculate the size, rather than
> hard coding it.
>
> Also, just as with c/s af292b41e9, there is no point forcing the CPU to set
> Access bits. Fix all remaining GDTs in Xen.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> ---
> CC: Jan Beulich <JBeulich@suse.com>
> CC: Wei Liu <wl@xen.org>
> CC: Roger Pau Monné <roger.pau@citrix.com>
>
> The trampoline GDT access bits were actually noticed when trying to clean up
> our boot time pagetables and map the trampoline read-only.
> ---
> xen/arch/x86/boot/head.S | 2 +-
> xen/arch/x86/boot/trampoline.S | 15 ++++++++-------
> xen/arch/x86/x86_64/kexec_reloc.S | 4 ++--
> 3 files changed, 11 insertions(+), 10 deletions(-)
>
> diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
> index 26b680521d..9fdb9b3954 100644
> --- a/xen/arch/x86/boot/head.S
> +++ b/xen/arch/x86/boot/head.S
> @@ -129,7 +129,7 @@ multiboot2_header:
>
> .word 0
> gdt_boot_descr:
> - .word 7*8-1
> + .word .Ltramopline_gdt_end - trampoline_gdt - 1
> gdt_boot_base:
> .long sym_offs(trampoline_gdt)
> .long 0 /* Needed for 64-bit lgdt */
> diff --git a/xen/arch/x86/boot/trampoline.S b/xen/arch/x86/boot/trampoline.S
> index 7c6a2328d2..1761fc1213 100644
> --- a/xen/arch/x86/boot/trampoline.S
> +++ b/xen/arch/x86/boot/trampoline.S
> @@ -63,22 +63,23 @@ trampoline_gdt:
> /* 0x0000: unused */
> .quad 0x0000000000000000
> /* 0x0008: ring 0 code, 32-bit mode */
> - .quad 0x00cf9a000000ffff
> + .quad 0x00cf9b000000ffff
> /* 0x0010: ring 0 code, 64-bit mode */
> - .quad 0x00af9a000000ffff
> + .quad 0x00af9b000000ffff
> /* 0x0018: ring 0 data */
> - .quad 0x00cf92000000ffff
> + .quad 0x00cf93000000ffff
> /* 0x0020: real-mode code @ BOOT_TRAMPOLINE */
> .long 0x0000ffff
> - .long 0x00009a00
> + .long 0x00009b00
> /* 0x0028: real-mode data @ BOOT_TRAMPOLINE */
> .long 0x0000ffff
> - .long 0x00009200
> + .long 0x00009300
> /*
> * 0x0030: ring 0 Xen data, 16 MiB size, base
> * address is computed at runtime.
> */
> - .quad 0x00c0920000000fff
> + .quad 0x00c0930000000fff
> +.Ltramopline_gdt_end:
With the typo here fixed
Reviewed-by: Jan Beulich <jbeulich@suse.com>
But may I talk you into ...
> --- a/xen/arch/x86/x86_64/kexec_reloc.S
> +++ b/xen/arch/x86/x86_64/kexec_reloc.S
> @@ -182,8 +182,8 @@ compat_mode_gdt_desc:
> .align 8
> compat_mode_gdt:
> .quad 0x0000000000000000 /* null */
> - .quad 0x00cf92000000ffff /* 0x0008 ring 0 data */
> - .quad 0x00cf9a000000ffff /* 0x0010 ring 0 code, compatibility */
> + .quad 0x00cf93000000ffff /* 0x0008 ring 0 data */
> + .quad 0x00cf9b000000ffff /* 0x0010 ring 0 code, compatibility */
... introducing a similar "end" label here and using it at
compat_mode_gdt_desc (the R-b above stands with that change)?
Jan
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^ permalink raw reply [flat|nested] 8+ messages in thread
* [Xen-devel] [PATCH] x86/boot: Reposition trampoline data
2019-08-19 13:42 [Xen-devel] [PATCH] x86/boot: Various bits of trampoline cleanup Andrew Cooper
2019-08-19 13:42 ` [Xen-devel] [PATCH] x86/boot: Further minor GDT corrections Andrew Cooper
@ 2019-08-19 13:42 ` Andrew Cooper
2019-08-19 16:02 ` David Woodhouse
2019-08-27 14:50 ` Jan Beulich
2019-08-19 13:42 ` [Xen-devel] [PATCH] x86/boot: Drop all use of lmsw Andrew Cooper
2 siblings, 2 replies; 8+ messages in thread
From: Andrew Cooper @ 2019-08-19 13:42 UTC (permalink / raw)
To: Xen-devel; +Cc: Andrew Cooper, Wei Liu, Jan Beulich, Roger Pau Monné
... to separate code from data. In particular, trampoline_realmode_entry's
write to trampoline_cpu_started clobbers the I-cache line containing
trampoline_protmode_entry, which won't be great for AP startup.
Reformat the comments for trampoline_gdt to reduce their volume.
No functional change.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wl@xen.org>
CC: Roger Pau Monné <roger.pau@citrix.com>
---
xen/arch/x86/boot/trampoline.S | 67 ++++++++++++++++++------------------------
1 file changed, 28 insertions(+), 39 deletions(-)
diff --git a/xen/arch/x86/boot/trampoline.S b/xen/arch/x86/boot/trampoline.S
index 1761fc1213..1b11b4757a 100644
--- a/xen/arch/x86/boot/trampoline.S
+++ b/xen/arch/x86/boot/trampoline.S
@@ -59,45 +59,6 @@ GLOBAL(trampoline_realmode_entry)
lmsw %ax # CR0.PE = 1 (enter protected mode)
ljmpl $BOOT_CS32,$bootsym_rel(trampoline_protmode_entry,6)
-trampoline_gdt:
- /* 0x0000: unused */
- .quad 0x0000000000000000
- /* 0x0008: ring 0 code, 32-bit mode */
- .quad 0x00cf9b000000ffff
- /* 0x0010: ring 0 code, 64-bit mode */
- .quad 0x00af9b000000ffff
- /* 0x0018: ring 0 data */
- .quad 0x00cf93000000ffff
- /* 0x0020: real-mode code @ BOOT_TRAMPOLINE */
- .long 0x0000ffff
- .long 0x00009b00
- /* 0x0028: real-mode data @ BOOT_TRAMPOLINE */
- .long 0x0000ffff
- .long 0x00009300
- /*
- * 0x0030: ring 0 Xen data, 16 MiB size, base
- * address is computed at runtime.
- */
- .quad 0x00c0930000000fff
-.Ltramopline_gdt_end:
-
- .pushsection .trampoline_rel, "a"
- .long trampoline_gdt + BOOT_PSEUDORM_CS + 2 - .
- .long trampoline_gdt + BOOT_PSEUDORM_DS + 2 - .
- .popsection
-
-GLOBAL(trampoline_misc_enable_off)
- .quad 0
-
-GLOBAL(cpuid_ext_features)
- .long 0
-
-GLOBAL(trampoline_xen_phys_start)
- .long 0
-
-GLOBAL(trampoline_cpu_started)
- .byte 0
-
.code32
trampoline_protmode_entry:
/* Set up a few descriptors: on entry only CS is guaranteed good. */
@@ -186,6 +147,34 @@ idt_48: .word 0, 0, 0 # base = limit = 0
gdt_48: .word .Ltramopline_gdt_end - trampoline_gdt - 1
.long bootsym_rel(trampoline_gdt,4)
+trampoline_gdt:
+ .quad 0x0000000000000000 /* 0x0000: unused */
+ .quad 0x00cf9b000000ffff /* 0x0008: ring 0 code, 32-bit mode */
+ .quad 0x00af9b000000ffff /* 0x0010: ring 0 code, 64-bit mode */
+ .quad 0x00cf93000000ffff /* 0x0018: ring 0 data */
+ .quad 0x00009b000000ffff /* 0x0020: real-mode code @ BOOT_TRAMPOLINE */
+ .quad 0x000093000000ffff /* 0x0028: real-mode data @ BOOT_TRAMPOLINE */
+ .quad 0x00c0930000000fff /* 0x0030: ring 0 Xen data, 16M @ XEN */
+.Ltramopline_gdt_end:
+
+ /* Relocations for trampoline Real Mode segments. */
+ .pushsection .trampoline_rel, "a"
+ .long trampoline_gdt + BOOT_PSEUDORM_CS + 2 - .
+ .long trampoline_gdt + BOOT_PSEUDORM_DS + 2 - .
+ .popsection
+
+GLOBAL(trampoline_misc_enable_off)
+ .quad 0
+
+GLOBAL(cpuid_ext_features)
+ .long 0
+
+GLOBAL(trampoline_xen_phys_start)
+ .long 0
+
+GLOBAL(trampoline_cpu_started)
+ .byte 0
+
/* The first page of trampoline is permanent, the rest boot-time only. */
/* Reuse the boot trampoline on the 1st trampoline page as stack for wakeup. */
.equ wakeup_stack, trampoline_start + PAGE_SIZE
--
2.11.0
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^ permalink raw reply related [flat|nested] 8+ messages in thread* Re: [Xen-devel] [PATCH] x86/boot: Reposition trampoline data
2019-08-19 13:42 ` [Xen-devel] [PATCH] x86/boot: Reposition trampoline data Andrew Cooper
@ 2019-08-19 16:02 ` David Woodhouse
2019-08-27 14:50 ` Jan Beulich
1 sibling, 0 replies; 8+ messages in thread
From: David Woodhouse @ 2019-08-19 16:02 UTC (permalink / raw)
To: Andrew Cooper, Xen-devel; +Cc: Jan Beulich, Wei Liu, Roger Pau Monné
[-- Attachment #1.1: Type: text/plain, Size: 4295 bytes --]
On Mon, 2019-08-19 at 14:42 +0100, Andrew Cooper wrote:
> ... to separate code from data. In particular,
> trampoline_realmode_entry's
> write to trampoline_cpu_started clobbers the I-cache line containing
> trampoline_protmode_entry, which won't be great for AP startup.
>
> Reformat the comments for trampoline_gdt to reduce their volume.
>
> No functional change.
Please, let's not do this one until my other boot cleanups have landed.
It just hurts. I have also reordered some of these for functional
reasons, because they are used in different contexts (and end up in
completely different trampolines).
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> ---
> CC: Jan Beulich <JBeulich@suse.com>
> CC: Wei Liu <wl@xen.org>
> CC: Roger Pau Monné <roger.pau@citrix.com>
> ---
> xen/arch/x86/boot/trampoline.S | 67 ++++++++++++++++++------------
> ------------
> 1 file changed, 28 insertions(+), 39 deletions(-)
>
> diff --git a/xen/arch/x86/boot/trampoline.S
> b/xen/arch/x86/boot/trampoline.S
> index 1761fc1213..1b11b4757a 100644
> --- a/xen/arch/x86/boot/trampoline.S
> +++ b/xen/arch/x86/boot/trampoline.S
> @@ -59,45 +59,6 @@ GLOBAL(trampoline_realmode_entry)
> lmsw %ax # CR0.PE = 1 (enter
> protected mode)
> ljmpl $BOOT_CS32,$bootsym_rel(trampoline_protmode_entry,6)
>
> -trampoline_gdt:
> - /* 0x0000: unused */
> - .quad 0x0000000000000000
> - /* 0x0008: ring 0 code, 32-bit mode */
> - .quad 0x00cf9b000000ffff
> - /* 0x0010: ring 0 code, 64-bit mode */
> - .quad 0x00af9b000000ffff
> - /* 0x0018: ring 0 data */
> - .quad 0x00cf93000000ffff
> - /* 0x0020: real-mode code @ BOOT_TRAMPOLINE */
> - .long 0x0000ffff
> - .long 0x00009b00
> - /* 0x0028: real-mode data @ BOOT_TRAMPOLINE */
> - .long 0x0000ffff
> - .long 0x00009300
> - /*
> - * 0x0030: ring 0 Xen data, 16 MiB size, base
> - * address is computed at runtime.
> - */
> - .quad 0x00c0930000000fff
> -.Ltramopline_gdt_end:
> -
> - .pushsection .trampoline_rel, "a"
> - .long trampoline_gdt + BOOT_PSEUDORM_CS + 2 - .
> - .long trampoline_gdt + BOOT_PSEUDORM_DS + 2 - .
> - .popsection
> -
> -GLOBAL(trampoline_misc_enable_off)
> - .quad 0
> -
> -GLOBAL(cpuid_ext_features)
> - .long 0
> -
> -GLOBAL(trampoline_xen_phys_start)
> - .long 0
> -
> -GLOBAL(trampoline_cpu_started)
> - .byte 0
> -
> .code32
> trampoline_protmode_entry:
> /* Set up a few descriptors: on entry only CS is guaranteed
> good. */
> @@ -186,6 +147,34 @@ idt_48: .word 0, 0, 0 # base = limit = 0
> gdt_48: .word .Ltramopline_gdt_end - trampoline_gdt - 1
> .long bootsym_rel(trampoline_gdt,4)
>
> +trampoline_gdt:
> + .quad 0x0000000000000000 /* 0x0000: unused */
> + .quad 0x00cf9b000000ffff /* 0x0008: ring 0 code, 32-bit
> mode */
> + .quad 0x00af9b000000ffff /* 0x0010: ring 0 code, 64-bit
> mode */
> + .quad 0x00cf93000000ffff /* 0x0018: ring 0 data */
> + .quad 0x00009b000000ffff /* 0x0020: real-mode code @
> BOOT_TRAMPOLINE */
> + .quad 0x000093000000ffff /* 0x0028: real-mode data @
> BOOT_TRAMPOLINE */
> + .quad 0x00c0930000000fff /* 0x0030: ring 0 Xen data, 16M @
> XEN */
> +.Ltramopline_gdt_end:
> +
> + /* Relocations for trampoline Real Mode segments. */
> + .pushsection .trampoline_rel, "a"
> + .long trampoline_gdt + BOOT_PSEUDORM_CS + 2 - .
> + .long trampoline_gdt + BOOT_PSEUDORM_DS + 2 - .
> + .popsection
> +
> +GLOBAL(trampoline_misc_enable_off)
> + .quad 0
> +
> +GLOBAL(cpuid_ext_features)
> + .long 0
> +
> +GLOBAL(trampoline_xen_phys_start)
> + .long 0
> +
> +GLOBAL(trampoline_cpu_started)
> + .byte 0
> +
> /* The first page of trampoline is permanent, the rest boot-time
> only. */
> /* Reuse the boot trampoline on the 1st trampoline page as stack for
> wakeup. */
> .equ wakeup_stack, trampoline_start + PAGE_SIZE
[-- Attachment #1.2: smime.p7s --]
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[-- Attachment #2: Type: text/plain, Size: 157 bytes --]
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^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [Xen-devel] [PATCH] x86/boot: Reposition trampoline data
2019-08-19 13:42 ` [Xen-devel] [PATCH] x86/boot: Reposition trampoline data Andrew Cooper
2019-08-19 16:02 ` David Woodhouse
@ 2019-08-27 14:50 ` Jan Beulich
1 sibling, 0 replies; 8+ messages in thread
From: Jan Beulich @ 2019-08-27 14:50 UTC (permalink / raw)
To: Andrew Cooper; +Cc: Xen-devel, Wei Liu, Roger Pau Monné
On 19.08.2019 15:42, Andrew Cooper wrote:
> ... to separate code from data. In particular, trampoline_realmode_entry's
> write to trampoline_cpu_started clobbers the I-cache line containing
> trampoline_protmode_entry, which won't be great for AP startup.
>
> Reformat the comments for trampoline_gdt to reduce their volume.
>
> No functional change.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
, ... subject to David's concern wrt his series.
Jan
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^ permalink raw reply [flat|nested] 8+ messages in thread
* [Xen-devel] [PATCH] x86/boot: Drop all use of lmsw
2019-08-19 13:42 [Xen-devel] [PATCH] x86/boot: Various bits of trampoline cleanup Andrew Cooper
2019-08-19 13:42 ` [Xen-devel] [PATCH] x86/boot: Further minor GDT corrections Andrew Cooper
2019-08-19 13:42 ` [Xen-devel] [PATCH] x86/boot: Reposition trampoline data Andrew Cooper
@ 2019-08-19 13:42 ` Andrew Cooper
2019-08-27 14:52 ` Jan Beulich
2 siblings, 1 reply; 8+ messages in thread
From: Andrew Cooper @ 2019-08-19 13:42 UTC (permalink / raw)
To: Xen-devel; +Cc: Andrew Cooper, Wei Liu, Jan Beulich, Roger Pau Monné
lmsw is an obsolete relic of the 286 processor - so much so that it even lacks
intercept assistance on AMD processors.
Use a plain mov to %cr0 which is easier to follow, certainly faster to
virtualise on AMD hardware, and almost certainly a faster microcode path in
real hardware.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wl@xen.org>
CC: Roger Pau Monné <roger.pau@citrix.com>
---
xen/arch/x86/boot/trampoline.S | 12 ++++++------
xen/arch/x86/boot/wakeup.S | 5 +++--
2 files changed, 9 insertions(+), 8 deletions(-)
diff --git a/xen/arch/x86/boot/trampoline.S b/xen/arch/x86/boot/trampoline.S
index 1b11b4757a..89f841331d 100644
--- a/xen/arch/x86/boot/trampoline.S
+++ b/xen/arch/x86/boot/trampoline.S
@@ -54,9 +54,10 @@ GLOBAL(trampoline_realmode_entry)
lidt bootsym(idt_48)
lgdt bootsym(gdt_48)
mov $1,%bl # EBX != 0 indicates we are an AP
- xor %ax, %ax
- inc %ax
- lmsw %ax # CR0.PE = 1 (enter protected mode)
+
+ mov $X86_CR0_PE, %eax
+ mov %eax, %cr0
+
ljmpl $BOOT_CS32,$bootsym_rel(trampoline_protmode_entry,6)
.code32
@@ -252,9 +253,8 @@ trampoline_boot_cpu_entry:
lgdt bootsym(gdt_48)
/* Enter protected mode, and flush insn queue. */
- xor %ax,%ax
- inc %ax
- lmsw %ax # CR0.PE = 1 (enter protected mode)
+ mov $X86_CR0_PE, %eax
+ mov %eax, %cr0
/* Load proper protected-mode values into all segment registers. */
ljmpl $BOOT_CS32,$bootsym_rel(1f,6)
diff --git a/xen/arch/x86/boot/wakeup.S b/xen/arch/x86/boot/wakeup.S
index e3cb9e033a..2af6c6017c 100644
--- a/xen/arch/x86/boot/wakeup.S
+++ b/xen/arch/x86/boot/wakeup.S
@@ -51,8 +51,9 @@ ENTRY(wakeup_start)
lidt wakesym(idt_48)
lgdt wakesym(gdt_48)
- movw $1, %ax
- lmsw %ax # Turn on CR0.PE
+ mov $X86_CR0_PE, %eax
+ mov %eax, %cr0
+
ljmpl $BOOT_CS32, $bootsym_rel(wakeup_32, 6)
/* This code uses an extended set of video mode numbers. These include:
--
2.11.0
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^ permalink raw reply related [flat|nested] 8+ messages in thread* Re: [Xen-devel] [PATCH] x86/boot: Drop all use of lmsw
2019-08-19 13:42 ` [Xen-devel] [PATCH] x86/boot: Drop all use of lmsw Andrew Cooper
@ 2019-08-27 14:52 ` Jan Beulich
0 siblings, 0 replies; 8+ messages in thread
From: Jan Beulich @ 2019-08-27 14:52 UTC (permalink / raw)
To: Andrew Cooper; +Cc: Xen-devel, Wei Liu, Roger Pau Monné
On 19.08.2019 15:42, Andrew Cooper wrote:
> lmsw is an obsolete relic of the 286 processor - so much so that it even lacks
> intercept assistance on AMD processors.
>
> Use a plain mov to %cr0 which is easier to follow, certainly faster to
> virtualise on AMD hardware, and almost certainly a faster microcode path in
> real hardware.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
with one further suggestion:
> --- a/xen/arch/x86/boot/trampoline.S
> +++ b/xen/arch/x86/boot/trampoline.S
> @@ -54,9 +54,10 @@ GLOBAL(trampoline_realmode_entry)
> lidt bootsym(idt_48)
> lgdt bootsym(gdt_48)
> mov $1,%bl # EBX != 0 indicates we are an AP
> - xor %ax, %ax
> - inc %ax
> - lmsw %ax # CR0.PE = 1 (enter protected mode)
> +
> + mov $X86_CR0_PE, %eax
> + mov %eax, %cr0
Why don't you use %ebx here, allowing the move to %bl to be
dropped at the same time?
Jan
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