[Qemu-devel] [FIX] X86 CPU topology broken in KVM mode

[Qemu-devel] [FIX] X86 CPU topology broken in KVM mode

[Bharata B Rao]

Hi,

Sometime back I posted a patch for fixing x86 CPU topology (
http://lists.gnu.org/archive/html/qemu-devel/2011-08/msg02022.html).
Here is the next version of the fix which addresses all but one
comment received during that post.

- Fixed code style issues
- Ensured that the fix doesn't break TCG mode
- I am not sure what is the problem with i486 as I haven't been able
to boot an i486 VM successfully, hence haven't attempted to fix this.

I have tested following scenarios and found the fix to be working fine.

KVM: (with --enable-kvm)
-smp sockets=1,cores=4,threads=2
-smp sockets=4,cores=4,threads=2
-cpu core2duo sockets=1,cores=4,threads=2
-cpu core2duo sockets=2,cores=4,threads=2

TCG: (without --enable-kvm)
-cpu core2duo sockets=1,cores=4,threads=2
-cpu core2duo sockets=2,cores=4,threads=2

Here is the updated patch which now applies against qemu.git.

********************
Fix apic id enumeration

apic id returned to guest kernel in ebx for cpuid(function=1) depends on
CPUX86State->cpuid_apic_id which gets populated after the cpuid information
is cached in the host kernel.

Fix this by setting cpuid_apic_id before cpuid information is passed to
the host kernel. This is done by moving the setting of cpuid_apic_id
to cpu_x86_init() where it will work for both KVM as well as TCG modes.

Signed-off-by: Bharata B Rao <bharata.rao@gmail.com>
---
 hw/pc.c              |    1 -
 target-i386/helper.c |    5 +++++
 2 files changed, 5 insertions(+), 1 deletion(-)

Index: qemu/hw/pc.c
===================================================================
--- qemu.orig/hw/pc.c
+++ qemu/hw/pc.c
@@ -933,7 +933,6 @@ static CPUState *pc_new_cpu(const char *
         exit(1);
     }
     if ((env->cpuid_features & CPUID_APIC) || smp_cpus > 1) {
-        env->cpuid_apic_id = env->cpu_index;
         env->apic_state = apic_init(env, env->cpuid_apic_id);
     }
     qemu_register_reset(pc_cpu_reset, env);
Index: qemu/target-i386/helper.c
===================================================================
--- qemu.orig/target-i386/helper.c
+++ qemu/target-i386/helper.c
@@ -1256,6 +1256,11 @@ CPUX86State *cpu_x86_init(const char *cp
         cpu_x86_close(env);
         return NULL;
     }
+
+    if (env->cpuid_features & CPUID_APIC) {
+        env->cpuid_apic_id = env->cpu_index;
+    }
+
     mce_init(env);

     qemu_init_vcpu(env);
*************************

Regards,
Bharata.
--
 http://bharata.sulekha.com/blog/posts.htm, http://raobharata.wordpress.com/

Re: [Qemu-devel] [FIX] X86 CPU topology broken in KVM mode

[Jan Kiszka]

On 2011-09-07 06:21, Bharata B Rao wrote:
> Hi,
> 
> Sometime back I posted a patch for fixing x86 CPU topology (
> http://lists.gnu.org/archive/html/qemu-devel/2011-08/msg02022.html).
> Here is the next version of the fix which addresses all but one
> comment received during that post.
> 
> - Fixed code style issues
> - Ensured that the fix doesn't break TCG mode
> - I am not sure what is the problem with i486 as I haven't been able
> to boot an i486 VM successfully, hence haven't attempted to fix this.

-smp 2 -cpu i486 boots fine here (granted, I don't have some i486 SMP
kernel at hand).

> 
> I have tested following scenarios and found the fix to be working fine.
> 
> KVM: (with --enable-kvm)
> -smp sockets=1,cores=4,threads=2
> -smp sockets=4,cores=4,threads=2
> -cpu core2duo sockets=1,cores=4,threads=2
> -cpu core2duo sockets=2,cores=4,threads=2
> 
> TCG: (without --enable-kvm)
> -cpu core2duo sockets=1,cores=4,threads=2
> -cpu core2duo sockets=2,cores=4,threads=2
> 
> Here is the updated patch which now applies against qemu.git.
> 
> ********************
> Fix apic id enumeration
> 
> apic id returned to guest kernel in ebx for cpuid(function=1) depends on
> CPUX86State->cpuid_apic_id which gets populated after the cpuid information
> is cached in the host kernel.
> 
> Fix this by setting cpuid_apic_id before cpuid information is passed to
> the host kernel. This is done by moving the setting of cpuid_apic_id
> to cpu_x86_init() where it will work for both KVM as well as TCG modes.
> 
> Signed-off-by: Bharata B Rao <bharata.rao@gmail.com>
> ---
>  hw/pc.c              |    1 -
>  target-i386/helper.c |    5 +++++
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> Index: qemu/hw/pc.c
> ===================================================================
> --- qemu.orig/hw/pc.c
> +++ qemu/hw/pc.c
> @@ -933,7 +933,6 @@ static CPUState *pc_new_cpu(const char *
>          exit(1);
>      }
>      if ((env->cpuid_features & CPUID_APIC) || smp_cpus > 1) {
> -        env->cpuid_apic_id = env->cpu_index;
>          env->apic_state = apic_init(env, env->cpuid_apic_id);
>      }
>      qemu_register_reset(pc_cpu_reset, env);
> Index: qemu/target-i386/helper.c
> ===================================================================
> --- qemu.orig/target-i386/helper.c
> +++ qemu/target-i386/helper.c
> @@ -1256,6 +1256,11 @@ CPUX86State *cpu_x86_init(const char *cp
>          cpu_x86_close(env);
>          return NULL;
>      }
> +
> +    if (env->cpuid_features & CPUID_APIC) {

|| smp_cpus > 1

Should be obvious when looking at the hunk you took this from.

> +        env->cpuid_apic_id = env->cpu_index;
> +    }
> +
>      mce_init(env);
> 
>      qemu_init_vcpu(env);
> *************************
> 
> Regards,
> Bharata.
> --
>  http://bharata.sulekha.com/blog/posts.htm, http://raobharata.wordpress.com/
> 
> 

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

Re: [Qemu-devel] [FIX] X86 CPU topology broken in KVM mode

[Bharata B Rao]

On Wed, Sep 7, 2011 at 1:37 PM, Jan Kiszka <jan.kiszka@siemens.com> wrote:
> On 2011-09-07 06:21, Bharata B Rao wrote:
>> - I am not sure what is the problem with i486 as I haven't been able
>> to boot an i486 VM successfully, hence haven't attempted to fix this.
>
> -smp 2 -cpu i486 boots fine here (granted, I don't have some i486 SMP
> kernel at hand).

I am getting "Unable to find x86 CPU definition" error with -cpu i486.
Need to investigate more.

>> +
>> +    if (env->cpuid_features & CPUID_APIC) {
>
> || smp_cpus > 1
>
> Should be obvious when looking at the hunk you took this from.

Yes, but I thought no harm in initializing it for uni processor case too, no ?

Regards,
Bharata.

Re: [Qemu-devel] [FIX] X86 CPU topology broken in KVM mode

[Jan Kiszka]

On 2011-09-07 10:19, Bharata B Rao wrote:
> On Wed, Sep 7, 2011 at 1:37 PM, Jan Kiszka <jan.kiszka@siemens.com> wrote:
>> On 2011-09-07 06:21, Bharata B Rao wrote:
>>> - I am not sure what is the problem with i486 as I haven't been able
>>> to boot an i486 VM successfully, hence haven't attempted to fix this.
>>
>> -smp 2 -cpu i486 boots fine here (granted, I don't have some i486 SMP
>> kernel at hand).
> 
> I am getting "Unable to find x86 CPU definition" error with -cpu i486.
> Need to investigate more.

Err, sorry: -cpu 486

> 
>>> +
>>> +    if (env->cpuid_features & CPUID_APIC) {
>>
>> || smp_cpus > 1
>>
>> Should be obvious when looking at the hunk you took this from.
> 
> Yes, but I thought no harm in initializing it for uni processor case too, no ?

486 CPUs do not have the CPUID_APIC feature set as they do not include a
local APIC. But those SMP systems have external APICs.

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

Re: [Qemu-devel] [FIX] X86 CPU topology broken in KVM mode

[Anthony Liguori]

On 09/06/2011 11:21 PM, Bharata B Rao wrote:
> Hi,
>
> Sometime back I posted a patch for fixing x86 CPU topology (
> http://lists.gnu.org/archive/html/qemu-devel/2011-08/msg02022.html).
> Here is the next version of the fix which addresses all but one
> comment received during that post.
>
> - Fixed code style issues
> - Ensured that the fix doesn't break TCG mode
> - I am not sure what is the problem with i486 as I haven't been able
> to boot an i486 VM successfully, hence haven't attempted to fix this.
>
> I have tested following scenarios and found the fix to be working fine.
>
> KVM: (with --enable-kvm)
> -smp sockets=1,cores=4,threads=2
> -smp sockets=4,cores=4,threads=2
> -cpu core2duo sockets=1,cores=4,threads=2
> -cpu core2duo sockets=2,cores=4,threads=2
>
> TCG: (without --enable-kvm)
> -cpu core2duo sockets=1,cores=4,threads=2
> -cpu core2duo sockets=2,cores=4,threads=2
>
> Here is the updated patch which now applies against qemu.git.
>
> ********************
> Fix apic id enumeration
>
> apic id returned to guest kernel in ebx for cpuid(function=1) depends on
> CPUX86State->cpuid_apic_id which gets populated after the cpuid information
> is cached in the host kernel.
>
> Fix this by setting cpuid_apic_id before cpuid information is passed to
> the host kernel. This is done by moving the setting of cpuid_apic_id
> to cpu_x86_init() where it will work for both KVM as well as TCG modes.
>
> Signed-off-by: Bharata B Rao<bharata.rao@gmail.com>

Please post patches as top-level threads with [PATCH] in the subject. 
Please use git diff or better yet, git-send-email.

Regards,

Anthony Liguori

> ---
>   hw/pc.c              |    1 -
>   target-i386/helper.c |    5 +++++
>   2 files changed, 5 insertions(+), 1 deletion(-)
>
> Index: qemu/hw/pc.c
> ===================================================================
> --- qemu.orig/hw/pc.c
> +++ qemu/hw/pc.c
> @@ -933,7 +933,6 @@ static CPUState *pc_new_cpu(const char *
>           exit(1);
>       }
>       if ((env->cpuid_features&  CPUID_APIC) || smp_cpus>  1) {
> -        env->cpuid_apic_id = env->cpu_index;
>           env->apic_state = apic_init(env, env->cpuid_apic_id);
>       }
>       qemu_register_reset(pc_cpu_reset, env);
> Index: qemu/target-i386/helper.c
> ===================================================================
> --- qemu.orig/target-i386/helper.c
> +++ qemu/target-i386/helper.c
> @@ -1256,6 +1256,11 @@ CPUX86State *cpu_x86_init(const char *cp
>           cpu_x86_close(env);
>           return NULL;
>       }
> +
> +    if (env->cpuid_features&  CPUID_APIC) {
> +        env->cpuid_apic_id = env->cpu_index;
> +    }
> +
>       mce_init(env);
>
>       qemu_init_vcpu(env);
> *************************
>
> Regards,
> Bharata.
> --
>   http://bharata.sulekha.com/blog/posts.htm, http://raobharata.wordpress.com/
>

Re: [Qemu-devel] [FIX] X86 CPU topology broken in KVM mode

[Bharata B Rao]

On Wed, Sep 7, 2011 at 6:29 PM, Anthony Liguori <anthony@codemonkey.ws> wrote:
> On 09/06/2011 11:21 PM, Bharata B Rao wrote:
>>
>> Hi,
>>
> Please post patches as top-level threads with [PATCH] in the subject.

I posted a new thread and hence it has appeared as a top-level thread.

This was a fix and hence used [FIX], but if this mailing list expects
[PATCH], then will use it from next time.

> Please
> use git diff or better yet, git-send-email.

This was a small patch and hence used quilt. If you insist, I can use
git for the next post :)

Regards,
Bharata.

Re: [Qemu-devel] [FIX] X86 CPU topology broken in KVM mode

[Anthony Liguori]

On 09/07/2011 08:24 AM, Bharata B Rao wrote:
> On Wed, Sep 7, 2011 at 6:29 PM, Anthony Liguori<anthony@codemonkey.ws>  wrote:
>> On 09/06/2011 11:21 PM, Bharata B Rao wrote:
>>>
>>> Hi,
>>>
>> Please post patches as top-level threads with [PATCH] in the subject.
>
> I posted a new thread and hence it has appeared as a top-level thread.
>
> This was a fix and hence used [FIX], but if this mailing list expects
> [PATCH], then will use it from next time.
>
>> Please
>> use git diff or better yet, git-send-email.
>
> This was a small patch and hence used quilt. If you insist, I can use
> git for the next post :)

It's not strictly required, but git includes extra information in the 
patch it generates (base revision) which git-am can use to merge the 
patch via a 3way merge instead of patch fuzz.  That makes life a bit 
easier when you're applying a lot of patches.

Regards,

Anthony Liguori

>
> Regards,
> Bharata.
>