linux-kernel - Re: [PATCH RFC v1 07/18] x86/hyperv: extract partition ID from Microsoft Hypervisor if necessary

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Date:   Wed, 16 Sep 2020 16:32:43 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Wei Liu <wei.liu@...nel.org>,
        Linux on Hyper-V List <linux-hyperv@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        Linux Kernel List <linux-kernel@...r.kernel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Vineeth Pillai <viremana@...ux.microsoft.com>,
        Sunil Muthuswamy <sunilmut@...rosoft.com>,
        Nuno Das Neves <nudasnev@...rosoft.com>,
        Lillian Grassin-Drake <ligrassi@...rosoft.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
        "open list:GENERIC INCLUDE/ASM HEADER FILES" 
        <linux-arch@...r.kernel.org>
Subject: Re: [PATCH RFC v1 07/18] x86/hyperv: extract partition ID from
 Microsoft Hypervisor if necessary

On Tue, Sep 15, 2020 at 12:27:16PM +0200, Vitaly Kuznetsov wrote:
> Wei Liu <wei.liu@...nel.org> writes:
[...]
> >  
> > +void __init hv_get_partition_id(void)
> > +{
> > +	struct hv_get_partition_id *output_page;
> > +	int status;
> > +	unsigned long flags;
> > +
> > +	local_irq_save(flags);
> > +	output_page = *this_cpu_ptr(hyperv_pcpu_output_arg);
> > +	status = hv_do_hypercall(HVCALL_GET_PARTITION_ID, NULL, output_page) &
> > +		HV_HYPERCALL_RESULT_MASK;
> 
> Nit: in this case status is 'u16', we can define it as such (instead of
> signed int).

Fixed.

> 
> > +	if (status != HV_STATUS_SUCCESS)
> > +		pr_err("Failed to get partition ID: %d\n", status);
> > +	else
> > +		hv_current_partition_id = output_page->partition_id;
> > +	local_irq_restore(flags);
> > +
> > +	/* No point in proceeding if this failed */
> > +	BUG_ON(status != HV_STATUS_SUCCESS);
> > +}
> > +
> >  /*
> >   * This function is to be invoked early in the boot sequence after the
> >   * hypervisor has been detected.
> > @@ -440,6 +463,9 @@ void __init hyperv_init(void)
> >  
> >  	register_syscore_ops(&hv_syscore_ops);
> >  
> > +	if (hv_root_partition)
> > +		hv_get_partition_id();
> 
> According to TLFS, partition ID is available when AccessPartitionId
> privilege is granted. I'd suggest we check that instead of
> hv_root_partition (and we can set hv_current_partition_id to something
> like U64_MAX so we know it wasn't acuired). So the BUG_ON condition will
> move here:
> 
>         hv_get_partition_id();
>         BUG_ON(hv_root_partition && hv_current_partition_id == U64_MAX);
> 

Good point. I will reorganize this a bit.

Wei.