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 17:41:13 +0000
From:   "Sironi, Filippo" <sironi@...zon.de>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
CC:     "Graf, Alexander" <graf@...zon.com>,
        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. 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.

I'll repost.

Filippo





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