linux-kernel - Re: [PATCH v2 2/2] KVM: x86: Implement the arch-specific hook to report the VM UUID

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Date:   Thu, 16 May 2019 10:49:03 -0700
From:   Alexander Graf <graf@...zon.com>
To:     "Sironi, Filippo" <sironi@...zon.de>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
CC:     LKML <linux-kernel@...r.kernel.org>,
        KVM list <kvm@...r.kernel.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        "konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "vasu.srinivasan@...cle.com" <vasu.srinivasan@...cle.com>
Subject: Re: [PATCH v2 2/2] KVM: x86: Implement the arch-specific hook to
 report the VM UUID


On 16.05.19 10:41, Sironi, Filippo wrote:
>> On 16. May 2019, at 18:40, Boris Ostrovsky <boris.ostrovsky@...cle.com> wrote:
>>
>> 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@...zon.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@...zon.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 with
>>>>> 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=xen.git;a=blob;f=xen/common/kernel.c;h=612575430f1ce7faf5bd66e7a99f1758c63fb3cb;hb=HEAD#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.


Just keep it at NULL in kvm_para_get_uuid() and convert to the canonical
00000000-0000-0000-0000-000000000000 in uuid_show().

Alex