Messages in this thread | | | Subject | Re: [PATCH 1/1] ARM: LPAE: use phys_addr_t instead of unsigned long in outercache hooks | From | "Leizhen (ThunderTown)" <> | Date | Wed, 30 Dec 2020 16:08:16 +0800 |
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On 2020/12/29 18:51, Russell King - ARM Linux admin wrote: > On Tue, Dec 29, 2020 at 02:30:56PM +0800, Leizhen (ThunderTown) wrote: >> >> >> On 2020/12/26 20:13, Russell King - ARM Linux admin wrote: >>> On Fri, Dec 25, 2020 at 07:44:58PM +0800, Zhen Lei wrote: >>>> The outercache of some Hisilicon SOCs support physical addresses wider >>>> than 32-bits. The unsigned long datatype is not sufficient for mapping >>>> physical addresses >= 4GB. The commit ad6b9c9d78b9 ("ARM: 6671/1: LPAE: >>>> use phys_addr_t instead of unsigned long in outercache functions") has >>>> already modified the outercache functions. But the parameters of the >>>> outercache hooks are not changed. This patch use phys_addr_t instead of >>>> unsigned long in outercache hooks: inv_range, clean_range, flush_range. >>>> >>>> To ensure the outercache that does not support LPAE works properly, do >>>> cast phys_addr_t to unsigned long by adding a middle-tier function. >>> >>> Please don't do that. The cast can be done inside the L2 functions >>> themselves without needing all these additional functions. >> >> OK. At first, I wanted to fit in like this: >> >> -static void l2c220_inv_range(unsigned long start, unsigned long end) >> +static void l2c220_inv_range(phys_addr_t lpae_start, phys_addr_t lpae_end) >> { >> + unsigned long start = lpae_start; >> + unsigned long end = lpae_end; > > It sounds like there should be a "but..." clause here. This is exactly > what I'm suggesting you should be doing. Currently, there's a silent > narrowing cast in every single caller of the outer_.*_range() functions > and you're only moving it from the callsites to inside the called > functions.
Okay, I will send v2 based on this idea.
> >>> We probably ought to also add some protection against addresses > 4GB, >>> although these are hot paths, so we don't want to add tests in these >>> functions. Maybe instead checking whether the system has memory above >>> 4GB while the L2 cache is being initialised would be a good idea? >> >> I'm sorry, I didn't quite understand what you meant. Currently, the >> biggest problem is the compilation problem. The sizeof(long) may be >> 32, and the 64-bit physical address cannot be transferred from outcache >> functions to outcache hooks. > > What I mean is that we really ought to warn if the L2C310 code tries to > initialise on a system where memory is above 4GB. However, it's very > unlikely that such a system exists, so it's probably fine not implement > a check, but it just feels fragile to be truncating the 64-bit address > to 32-bit on a kernel that _could_ support higher addresses, even though > that's exactly what is happening today (kind of by accident - I don't > think anyone realised.) >
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