* [PATCH kvm-unit-tests] i386: setup segment registers before percpu areas
@ 2020-06-24 14:14 Paolo Bonzini
2020-06-24 19:58 ` Nadav Amit
0 siblings, 1 reply; 4+ messages in thread
From: Paolo Bonzini @ 2020-06-24 14:14 UTC (permalink / raw)
To: kvm
The base of the percpu area is stored in the %gs base, and writing
to %gs destroys it. Move setup_segments earlier, before the %gs
base is written.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
x86/cstart.S | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/x86/cstart.S b/x86/cstart.S
index 5ad70b5..77dc34d 100644
--- a/x86/cstart.S
+++ b/x86/cstart.S
@@ -106,6 +106,7 @@ MSR_GS_BASE = 0xc0000101
.globl start
start:
mov $stacktop, %esp
+ setup_segments
push %ebx
call setup_multiboot
call setup_libcflat
@@ -118,7 +119,6 @@ start:
prepare_32:
lgdtl gdt32_descr
- setup_segments
mov %cr4, %eax
bts $4, %eax // pse
--
2.26.2
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH kvm-unit-tests] i386: setup segment registers before percpu areas
2020-06-24 14:14 [PATCH kvm-unit-tests] i386: setup segment registers before percpu areas Paolo Bonzini
@ 2020-06-24 19:58 ` Nadav Amit
2020-06-25 8:01 ` Paolo Bonzini
2020-06-25 11:09 ` Paolo Bonzini
0 siblings, 2 replies; 4+ messages in thread
From: Nadav Amit @ 2020-06-24 19:58 UTC (permalink / raw)
To: Paolo Bonzini; +Cc: kvm
> On Jun 24, 2020, at 7:14 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> The base of the percpu area is stored in the %gs base, and writing
> to %gs destroys it. Move setup_segments earlier, before the %gs
> base is written.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> x86/cstart.S | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/x86/cstart.S b/x86/cstart.S
> index 5ad70b5..77dc34d 100644
> --- a/x86/cstart.S
> +++ b/x86/cstart.S
> @@ -106,6 +106,7 @@ MSR_GS_BASE = 0xc0000101
> .globl start
> start:
> mov $stacktop, %esp
> + setup_segments
> push %ebx
> call setup_multiboot
> call setup_libcflat
> @@ -118,7 +119,6 @@ start:
>
> prepare_32:
> lgdtl gdt32_descr
> - setup_segments
>
> mov %cr4, %eax
> bts $4, %eax // pse
> —
> 2.26.2
As I said in a different thread, this change breaks my setup. It is better
not to make any assumption (or as few as possible) about the GDT content
after boot and load the GDTR before setting up the segments. So I prefer to
load the GDT before the segments. How about this change instead of yours?
-- >8 --
From: Nadav Amit <namit@vmware.com>
Date: Wed, 24 Jun 2020 19:50:36 +0000
Subject: [PATCH] x86: load gdt while loading segments
Signed-off-by: Nadav Amit <namit@vmware.com>
---
x86/cstart.S | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/x86/cstart.S b/x86/cstart.S
index dd33d4d..1d8b8ac 100644
--- a/x86/cstart.S
+++ b/x86/cstart.S
@@ -95,6 +95,8 @@ MSR_GS_BASE = 0xc0000101
.endm
.macro setup_segments
+ lgdtl gdt32_descr
+
mov $0x10, %ax
mov %ax, %ds
mov %ax, %es
@@ -106,6 +108,8 @@ MSR_GS_BASE = 0xc0000101
.globl start
start:
mov $stacktop, %esp
+ setup_segments
+
push %ebx
call setup_multiboot
call setup_libcflat
@@ -117,9 +121,6 @@ start:
jmpl $8, $start32
prepare_32:
- lgdtl gdt32_descr
- setup_segments
-
mov %cr4, %eax
bts $4, %eax // pse
mov %eax, %cr4
--
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH kvm-unit-tests] i386: setup segment registers before percpu areas
2020-06-24 19:58 ` Nadav Amit
@ 2020-06-25 8:01 ` Paolo Bonzini
2020-06-25 11:09 ` Paolo Bonzini
1 sibling, 0 replies; 4+ messages in thread
From: Paolo Bonzini @ 2020-06-25 8:01 UTC (permalink / raw)
To: Nadav Amit; +Cc: kvm
On 24/06/20 21:58, Nadav Amit wrote:
>> On Jun 24, 2020, at 7:14 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>
>> The base of the percpu area is stored in the %gs base, and writing
>> to %gs destroys it. Move setup_segments earlier, before the %gs
>> base is written.
>>
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>> ---
>> x86/cstart.S | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/x86/cstart.S b/x86/cstart.S
>> index 5ad70b5..77dc34d 100644
>> --- a/x86/cstart.S
>> +++ b/x86/cstart.S
>> @@ -106,6 +106,7 @@ MSR_GS_BASE = 0xc0000101
>> .globl start
>> start:
>> mov $stacktop, %esp
>> + setup_segments
>> push %ebx
>> call setup_multiboot
>> call setup_libcflat
>> @@ -118,7 +119,6 @@ start:
>>
>> prepare_32:
>> lgdtl gdt32_descr
>> - setup_segments
>>
>> mov %cr4, %eax
>> bts $4, %eax // pse
>> —
>> 2.26.2
>
> As I said in a different thread, this change breaks my setup. It is better
> not to make any assumption (or as few as possible) about the GDT content
> after boot and load the GDTR before setting up the segments. So I prefer to
> load the GDT before the segments. How about this change instead of yours?
Yes, this is better.
Paolo
> -- >8 --
>
> From: Nadav Amit <namit@vmware.com>
> Date: Wed, 24 Jun 2020 19:50:36 +0000
> Subject: [PATCH] x86: load gdt while loading segments
>
> Signed-off-by: Nadav Amit <namit@vmware.com>
> ---
> x86/cstart.S | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/x86/cstart.S b/x86/cstart.S
> index dd33d4d..1d8b8ac 100644
> --- a/x86/cstart.S
> +++ b/x86/cstart.S
> @@ -95,6 +95,8 @@ MSR_GS_BASE = 0xc0000101
> .endm
>
> .macro setup_segments
> + lgdtl gdt32_descr
> +
> mov $0x10, %ax
> mov %ax, %ds
> mov %ax, %es
> @@ -106,6 +108,8 @@ MSR_GS_BASE = 0xc0000101
> .globl start
> start:
> mov $stacktop, %esp
> + setup_segments
> +
> push %ebx
> call setup_multiboot
> call setup_libcflat
> @@ -117,9 +121,6 @@ start:
> jmpl $8, $start32
>
> prepare_32:
> - lgdtl gdt32_descr
> - setup_segments
> -
> mov %cr4, %eax
> bts $4, %eax // pse
> mov %eax, %cr4
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH kvm-unit-tests] i386: setup segment registers before percpu areas
2020-06-24 19:58 ` Nadav Amit
2020-06-25 8:01 ` Paolo Bonzini
@ 2020-06-25 11:09 ` Paolo Bonzini
1 sibling, 0 replies; 4+ messages in thread
From: Paolo Bonzini @ 2020-06-25 11:09 UTC (permalink / raw)
To: Nadav Amit; +Cc: kvm
On 24/06/20 21:58, Nadav Amit wrote:
> From: Nadav Amit <namit@vmware.com>
> Date: Wed, 24 Jun 2020 19:50:36 +0000
> Subject: [PATCH] x86: load gdt while loading segments
>
> Signed-off-by: Nadav Amit <namit@vmware.com>
> ---
> x86/cstart.S | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/x86/cstart.S b/x86/cstart.S
> index dd33d4d..1d8b8ac 100644
> --- a/x86/cstart.S
> +++ b/x86/cstart.S
> @@ -95,6 +95,8 @@ MSR_GS_BASE = 0xc0000101
> .endm
>
> .macro setup_segments
> + lgdtl gdt32_descr
> +
> mov $0x10, %ax
> mov %ax, %ds
> mov %ax, %es
> @@ -106,6 +108,8 @@ MSR_GS_BASE = 0xc0000101
> .globl start
> start:
> mov $stacktop, %esp
> + setup_segments
> +
> push %ebx
> call setup_multiboot
> call setup_libcflat
> @@ -117,9 +121,6 @@ start:
> jmpl $8, $start32
>
> prepare_32:
> - lgdtl gdt32_descr
> - setup_segments
> -
> mov %cr4, %eax
> bts $4, %eax // pse
> mov %eax, %cr4
> --
The GDT is already loaded elsewhere for APs, but the gist of the patch
is good. I'll send v2
Paolo
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2020-06-25 11:09 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2020-06-24 14:14 [PATCH kvm-unit-tests] i386: setup segment registers before percpu areas Paolo Bonzini
2020-06-24 19:58 ` Nadav Amit
2020-06-25 8:01 ` Paolo Bonzini
2020-06-25 11:09 ` Paolo Bonzini
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