linux-kernel - Re: efi_enabled(EFI

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Message-ID: <572576E2.7060508@linaro.org>
Date:	Sun, 1 May 2016 11:24:18 +0800
From:	Shannon Zhao <shannon.zhao@...aro.org>
To:	Matt Fleming <matt@...eblueprint.co.uk>
Cc:	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Stefano Stabellini <sstabellini@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	"Luis R. Rodriguez" <mcgrof@...nel.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Xen Devel <Xen-devel@...ts.xensource.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-next@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: efi_enabled(EFI_PARAVIRT) use

On 2016年05月01日 04:44, Matt Fleming wrote:
>> While I still have a question, in this patch we use
>> > efi_enabled(EFI_PARAVIRT) as a condition to make fdt_find_uefi_params()
>> > and efi_get_fdt_params() execute different ways. So it needs to find a
>> > new condition for that if we need to get rid of EFI_PARAVIRT. One I
>> > think is that xen_initial_domain() check. Is that fine?
> Hmm... why do you actually need to check whether you're running on a
> PV machine in fdt_find_uefi_params()?
Because the UEFI params for Dom0 are located under /hypervisor/uefi node
instead of /chosen. So it needs to check whether it's a Dom0 then search
and parse different node with different params arrays.

> Can't you infer that from the DT
> params you discover?
> 

> I could understand maybe only accepting the "xen,uefi-system-table"
> property if IS_ENABLED(CONFIG_XEN) but surely you don't also need to
> filter based on whether you're booting a PV kernel?
> 
> Let me put it this way: when would you see "xen,uefi-system-table" and
> *not* be booting a PV kernel?
So it still needs add another check to firstly parse the fdt to see if
there is "xen,uefi-system-table" under /hypervisor/uefi node, right? I
think it's a bit redundant compared with xen_initial_domain().

Thanks,
-- 
Shannon