linux-kernel - Re: [PATCH 7/9] xen/x86: hook up xen

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Date:   Wed, 29 Sep 2021 07:45:47 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Jan Beulich <jbeulich@...e.com>
Cc:     Stefano Stabellini <sstabellini@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [PATCH 7/9] xen/x86: hook up xen_banner() also for PVH

On 23.09.21 17:31, Jan Beulich wrote:
> On 23.09.2021 17:25, Juergen Gross wrote:
>> On 23.09.21 17:19, Jan Beulich wrote:
>>> On 23.09.2021 17:15, Juergen Gross wrote:
>>>> On 23.09.21 17:10, Jan Beulich wrote:
>>>>> On 23.09.2021 16:59, Juergen Gross wrote:
>>>>>> On 07.09.21 12:11, Jan Beulich wrote:
>>>>>>> This was effectively lost while dropping PVHv1 code. Move the function
>>>>>>> and arrange for it to be called the same way as done in PV mode. Clearly
>>>>>>> this then needs re-introducing the XENFEAT_mmu_pt_update_preserve_ad
>>>>>>> check that was recently removed, as that's a PV-only feature.
>>>>>>>
>>>>>>> Signed-off-by: Jan Beulich <jbeulich@...e.com>
>>>>>>>
>>>>>>> --- a/arch/x86/xen/enlighten.c
>>>>>>> +++ b/arch/x86/xen/enlighten.c
>>>>>>> @@ -261,6 +261,18 @@ int xen_vcpu_setup(int cpu)
>>>>>>>      	return ((per_cpu(xen_vcpu, cpu) == NULL) ? -ENODEV : 0);
>>>>>>>      }
>>>>>>>      
>>>>>>> +void __init xen_banner(void)
>>>>>>> +{
>>>>>>> +	unsigned version = HYPERVISOR_xen_version(XENVER_version, NULL);
>>>>>>> +	struct xen_extraversion extra;
>>>>>>
>>>>>> Please add a blank line here.
>>>>>
>>>>> Oops.
>>>>>
>>>>>>> +	HYPERVISOR_xen_version(XENVER_extraversion, &extra);
>>>>>>> +
>>>>>>> +	pr_info("Booting paravirtualized kernel on %s\n", pv_info.name);
>>>>>>
>>>>>> Is this correct? I don't think the kernel needs to be paravirtualized
>>>>>> with PVH (at least not to the same extend as for PV).
>>>>>
>>>>> What else do you suggest the message to say? Simply drop
>>>>> "paravirtualized"? To some extent it is applicable imo, further
>>>>> qualified by pv_info.name. And that's how it apparently was with
>>>>> PVHv1.
>>>>
>>>> The string could be selected depending on CONFIG_XEN_PV.
>>>
>>> Hmm, now I'm confused: Doesn't this setting control whether the kernel
>>> can run in PV mode? If so, that functionality being present should have
>>> no effect on the functionality of the kernel when running in PVH mode.
>>> So what you suggest would end up in misleading information imo.
>>
>> Hmm, yes, I mixed "paravirtualized" with "capable to run
>> paravirtualized".
>>
>> So the string should depend on xen_pv_domain().
> 
> But that's already expressed by pv_info.name then being "Xen PV".

True. Okay, I'm fine with just dropping "paravirtualized".


Juergen

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