linux-kernel - Re: [PATCH v2 07/17] x86/hyperv: extract partition ID from Microsoft Hypervisor if necessary

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Message-ID: <20201113152152.omo6pljscvlrzpsc@liuwe-devbox-debian-v2>
Date:   Fri, 13 Nov 2020 15:21:52 +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 <nunodasneves@...ux.microsoft.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 v2 07/17] x86/hyperv: extract partition ID from Microsoft
 Hypervisor if necessary

On Thu, Nov 12, 2020 at 04:44:39PM +0100, Vitaly Kuznetsov wrote:
[...]
> > +void __init hv_get_partition_id(void)
> > +{
> > +	struct hv_get_partition_id *output_page;
> > +	u16 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;
> > +	if (status != HV_STATUS_SUCCESS)
> > +		pr_err("Failed to get partition ID: %d\n", status);
> > +	else
> > +		hv_current_partition_id = output_page->partition_id;
> 
> Nit: I'd suggest we simplify this to:
> 
> 	if (status != HV_STATUS_SUCCESS) {
> 		pr_err("Failed to get partition ID: %d\n", status);
> 		BUG();
> 	}
> 	hv_current_partition_id = output_page->partition_id;
> 
> and drop BUG_ON() below;
> 
> > +	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.
> > @@ -430,6 +453,9 @@ void __init hyperv_init(void)
> >  
> >  	register_syscore_ops(&hv_syscore_ops);
> >  
> > +	if (hv_root_partition)
> > +		hv_get_partition_id();
> > +
> 
> 
> We don't seem to check that the partition has AccessPartitionId
> privilege. While I guess that root partitions always have it, I'd
> suggest we write this as:
> 

Yes. Root should always have that permission. That's my understanding.

> 	if (cpuid_ebx(HYPERV_CPUID_FEATURES) & HV_ACCESS_PARTITION_ID)
> 		hv_get_partition_id();
> 
> 	BUG_ON(hv_root_partition && !hv_current_partition_id);
> 
> for correctness. Also, we need to make sure '0' is not a valid partition
> id and use e.g. -1 otherwise.
> 

I've changed both places.

Wei.