From: Huacai Chen <email@example.com> To: Paul Burton <firstname.lastname@example.org> Cc: Jiaxun Yang <email@example.com>, Paul Burton <firstname.lastname@example.org>, Ralf Baechle <email@example.com>, James Hogan <firstname.lastname@example.org>, Linux MIPS Mailing List <email@example.com>, "open list:MIPS" <firstname.lastname@example.org>, Fuxin Zhang <email@example.com>, Zhangjin Wu <firstname.lastname@example.org> Subject: Re: [PATCH] MIPS: Make sure ebase address is in KSEG0 Date: Tue, 26 Nov 2019 09:55:30 +0800 [thread overview] Message-ID: <CAAhV-H7kNQZ7Y77qmWusmvOmrySi9RU5JixcTuudR0MjUT9obw@mail.gmail.com> (raw) In-Reply-To: <email@example.com> Hi, Paul, On Tue, Nov 26, 2019 at 7:44 AM Paul Burton <firstname.lastname@example.org> wrote: > > Hi Huacai, > > On Sun, Nov 24, 2019 at 12:00:51PM +0800, Huacai Chen wrote: > > On Sat, Nov 23, 2019 at 2:11 PM Jiaxun Yang <email@example.com> wrote: > > > 于 2019年11月23日 GMT+08:00 下午1:08:38, Jiaxun Yang <firstname.lastname@example.org> 写到: > > > >于 2019年11月23日 GMT+08:00 上午2:47:31, Paul Burton <email@example.com> > > > >写到: > > > >>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://firstname.lastname@example.org/ > > > >> > > > >>Would that work for you? > > > > Now this patch has nothing to do with WG bit, > > Well, kind of. The 512MB limit is implicitly tied to the lack of a > functional WG bit. Yes, if CPU has no WG, we cannot use an ebase address above 512M, but a CPU with WG also has problems, please see the comments: * It shouldn't generally be in XKPhys on MIPS64 to avoid * hitting a poorly defined exception base for Cache Errors. So I think the warning is in order to tell us that we should avoid ebase address above 512M. And if we don't think this is a problem then let's simply remove the warning. > > > and also has nothing to do with Loongson, it just a problem with ebase > > address -- on any MIPSr2 platforms where ebase is dynamically > > allocated. > > Right, and the patch I proposed ensures that the allocation happens in > the low 512MB for systems without the WG bit, ie. in memory we can > access via kseg0. It just doesn't assume the memory is at physical > address 0 - it might be, but on some systems there might not even be > memory at 0. > > In practice we allocate memory bottom-up, so I'm not sure how you're > managing to see problems here anyway - allocations this early should > easily be within the low 512MB. If you could explain step by step what > actually goes wrong on your system that would be helpful. OK. Traditionally, Loongson-3's memory layout is like this: 0-240M: low memory 240-256M: reserved for firmware 256M-4G: holes, including PCI mem, MMIO registers, etc. 4G-...: high memory In practise, the kernel can hold as large as 60M memory (because of sparsemem), then initrd can be also as large as 60M (a full functional rootfs), swiotlb can be as large as 128M. Initrd and swiotlb is allocated before ebase, so in this extreme case, ebase address is above 512M. Huacai > > > 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). > > The warning can probably go away if my patch is applied, since the > allocation is constrained to the right memory region anyway. > > Thanks, > Paul
prev parent reply other threads:[~2019-11-26 1:49 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-11-21 11:30 Huacai Chen 2019-11-22 18:47 ` Paul Burton 2019-11-23 5:08 ` Jiaxun Yang 2019-11-23 6:11 ` Jiaxun Yang 2019-11-24 4:00 ` Huacai Chen 2019-11-25 23:42 ` Paul Burton 2019-11-26 1:55 ` Huacai Chen [this message]
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=CAAhV-H7kNQZ7Y77qmWusmvOmrySi9RU5JixcTuudR0MjUT9obw@mail.gmail.com \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --subject='Re: [PATCH] MIPS: Make sure ebase address is in KSEG0' \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).