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

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Message-ID: <3a9762a2-24e8-a842-862d-fadae563361d@oracle.com>
Date:   Thu, 16 May 2019 12:40:46 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Alexander Graf <graf@...zon.com>,
        "Sironi, Filippo" <sironi@...zon.de>
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 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