Re: [PATCH] MIPS: Make sure ebase address is in KSEG0

From: Huacai Chen <chenhc@lemote.com>
To: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Paul Burton <paulburton@kernel.org>,
	Paul Burton <paul.burton@mips.com>,
	Ralf Baechle <ralf@linux-mips.org>,
	James Hogan <jhogan@kernel.org>,
	Linux MIPS Mailing List <linux-mips@linux-mips.org>,
	"open list:MIPS" <linux-mips@vger.kernel.org>,
	Fuxin Zhang <zhangfx@lemote.com>,
	Zhangjin Wu <wuzhangjin@gmail.com>
Subject: Re: [PATCH] MIPS: Make sure ebase address is in KSEG0
Date: Sun, 24 Nov 2019 12:00:51 +0800	[thread overview]
Message-ID: <CAAhV-H4R1LqwLyehnTo89XPCeZo=ka=p29_rHVg=vJ_YiqqNCQ@mail.gmail.com> (raw)
In-Reply-To: <3C1D695B-09AA-4C2D-A94F-84DFC05C6F0C@flygoat.com>

Hi, Paul,

On Sat, Nov 23, 2019 at 2:11 PM Jiaxun Yang <jiaxun.yang@flygoat.com> wrote:
>
>
>
> 于 2019年11月23日 GMT+08:00 下午1:08:38, Jiaxun Yang <jiaxun.yang@flygoat.com> 写到:
> >
> >
> >于 2019年11月23日 GMT+08:00 上午2:47:31, Paul Burton <paulburton@kernel.org>
> >写到:
> >>Hi Huacai,
> >>
> >>On Thu, Nov 21, 2019 at 07:30:20PM +0800, Huacai Chen wrote:
> >>> Dynamically allocated ebase address above 0x20000000 can be
> >triggered
> >>> by some special physical memory layout, or just by a "big kernel +
> >>big
> >>> initrd + big swiotlb" configuration.
> >>>
> >>> For MIPS32, ebase address above 0x20000000 is unusable, for MIPS64
> >it
> >>> is usable but this case is warned. However, this warning is useless
> >>> because it is unfixable in a specific system configuration. So we
> >>just
> >>> use CKSEG0 as a fallback.
> >>
> >>I'd prefer that we don't assume there's memory at physical address
> >zero
> >>- that property doesn't hold for all systems.
> >>
> >>How about the change I suggested previously over here:
> >>
> >>https://lore.kernel.org/linux-mips/20191108191149.bbq3h4xp4famsh2n@lantea.localdomain/
> >>
> >>Would that work for you?
Now this patch has nothing to do with WG bit, and also has nothing to
do with Loongson, it just a problem with ebase address -- on any
MIPSr2 platforms where ebase is dynamically allocated.

In the comments it is said that ebase address above 0x20000000 (which
should be in XKphys) has problems to handle cache error. However, if
we really treat it as a problem, we should avoid it (not just a
warning); and if we don't think it is a problem, then we can remove
the warning (because the warning is unfixable in a specific system
configuration).

Huacai
> >
> >Hi Paul
> >
> >Our problem is, sometimes the ebase from firmware is totally a random
> >address,
> >even not inside the memory region. I'd prefer ignore address if it's
> >not valid since the warning here can't deal with it.
>
> I'm sorry. I was wrong. Please ignore the noise.
>
> Thanks
>
> >
> >Thanks.
> >>
> >>Thanks,
> >>    Paul
> >>
>
> --
> Jiaxun Yang