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

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Date:   Wed, 29 Sep 2021 09:28:26 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Juergen Gross <jgross@...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 29.09.2021 07:45, Juergen Gross wrote:
> 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".

Done. Do you want me to also make pr_info() vs printk(KERN_INFO ...)
consistent in the function at this occasion? If so - which of the two?

Jan