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From:   "Sironi, Filippo" <sironi@amazon.de>
To:     Boris Ostrovsky <boris.ostrovsky@oracle.com>
CC:     "Graf, Alexander" <graf@amazon.com>,
        LKML <linux-kernel@vger.kernel.org>,
        KVM list <kvm@vger.kernel.org>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        "cohuck@redhat.com" <cohuck@redhat.com>,
        "konrad.wilk@oracle.com" <konrad.wilk@oracle.com>,
        "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
        "vasu.srinivasan@oracle.com" <vasu.srinivasan@oracle.com>
Subject: Re: [PATCH v2 2/2] KVM: x86: Implement the arch-specific hook to
 report the VM UUID
Thread-Topic: [PATCH v2 2/2] KVM: x86: Implement the arch-specific hook to
 report the VM UUID
Thread-Index: AQHVCmgxSNZRVPU/lkacpReSlg9JAaZtyWCAgAAY24CAAAJ4gIAAErUAgAAQ44A=
Date:   Thu, 16 May 2019 17:41:13 +0000
Message-ID: <DD0087B6-094D-4D07-9C85-827881E3DDD0@amazon.de>
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> On 16. May 2019, at 18:40, Boris Ostrovsky <boris.ostrovsky@oracle.com> w=
rote:
> =

> On 5/16/19 11:33 AM, Alexander Graf wrote:
>> On 16.05.19 08:25, Sironi, Filippo wrote:
>>>> On 16. May 2019, at 15:56, Graf, Alexander <graf@amazon.com> wrote:
>>>> =

>>>> On 14.05.19 08:16, Filippo Sironi wrote:
>>>>> On x86, we report the UUID in DMI System Information (i.e., DMI Type =
1)
>>>>> as VM UUID.
>>>>> =

>>>>> Signed-off-by: Filippo Sironi <sironi@amazon.de>
>>>>> ---
>>>>> arch/x86/kernel/kvm.c | 7 +++++++
>>>>> 1 file changed, 7 insertions(+)
>>>>> =

>>>>> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
>>>>> index 5c93a65ee1e5..441cab08a09d 100644
>>>>> --- a/arch/x86/kernel/kvm.c
>>>>> +++ b/arch/x86/kernel/kvm.c
>>>>> @@ -25,6 +25,7 @@
>>>>> #include <linux/kernel.h>
>>>>> #include <linux/kvm_para.h>
>>>>> #include <linux/cpu.h>
>>>>> +#include <linux/dmi.h>
>>>>> #include <linux/mm.h>
>>>>> #include <linux/highmem.h>
>>>>> #include <linux/hardirq.h>
>>>>> @@ -694,6 +695,12 @@ bool kvm_para_available(void)
>>>>> }
>>>>> EXPORT_SYMBOL_GPL(kvm_para_available);
>>>>> =

>>>>> +const char *kvm_para_get_uuid(void)
>>>>> +{
>>>>> +	return dmi_get_system_info(DMI_PRODUCT_UUID);
>>>> This adds a new dependency on CONFIG_DMI. Probably best to guard it wi=
th
>>>> an #if IS_ENABLED(CONFIG_DMI).
>>>> =

>>>> The concept seems sound though.
>>>> =

>>>> Alex
>>> include/linux/dmi.h contains a dummy implementation of
>>> dmi_get_system_info that returns NULL if CONFIG_DMI isn't defined.
>> =

>> Oh, I missed that bit. Awesome! Less work :).
>> =

>> =

>>> This is enough unless we decide to return "<denied>" like in Xen.
>>> If then, we can have the check in the generic code to turn NULL
>>> into "<denied>".
>> =

>> Yes. Waiting for someone from Xen to answer this :)
> =

> Not sure I am answering your question but on Xen we return UUID value
> zero if access permissions are not sufficient. Not <denied>.
> =

> http://xenbits.xen.org/gitweb/?p=3Dxen.git;a=3Dblob;f=3Dxen/common/kernel=
.c;h=3D612575430f1ce7faf5bd66e7a99f1758c63fb3cb;hb=3DHEAD#l506
> =

> -boris

Then, I believe that returning 00000000-0000-0000-0000-000000000000
instead of NULL in the weak implementation of 1/2 and translating
NULL into 00000000-0000-0000-0000-000000000000 is the better approach.

I'll repost.

Filippo


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