Messages in this thread | | | Date | Sat, 30 Jan 2016 10:48:02 +0800 | From | Xishi Qiu <> | Subject | Re: [PATCH] arm64: Allow vmalloc regions to be set with set_memory_* |
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On 2016/1/29 19:02, Mark Rutland wrote:
> On Fri, Jan 29, 2016 at 09:21:40AM +0800, Xishi Qiu wrote: >> On 2016/1/28 22:27, Mark Rutland wrote: >>> On Thu, Jan 28, 2016 at 07:47:09PM +0800, Xishi Qiu wrote: >>>> Hi Mark, >>>> >>>> Is it safe in the following path? >>>> >>>> alloc the whole linear map section >>> >>> I don't understand what you mean by this, you will need to elaborate. >>> The terms "alloc" and "section" can mean a number of different things in >>> this context. >>> >>>> cpu A write something on it >>>> cpu B write something on it >>>> cpu C set read only flag and call flush_tlb_kernel_range() >>> >>> If you want to modify a portion of the linear map, this will not work. >>> Modfiying the linear map in this manner is not safe. >>> >>> If you want an alias of the linear map which was mapped using pages, and >>> you wanted to change that alias, that could work. >>> >> >> Hi Mark, >> >> I mean I change the whole section(maybe 1G?) in linear map. > > If you mean something that was mapped with a section (i.e. a block entry > in some level of page table), then no. The linear map is not open to > this kind of change, as portions of the region may be in use elsewhere > within Linux. > >> In our software, kernel create mapping(linear map) on special memory, >> and >> it is separated from buddy system, the service manage the special memory itself. > > This is not what the linear map is for. What exactly is this "special > memory"? > > Is it some persistent memory? > > Is it normal memory that you wish to use for some communication with > other agents and/or DMA? > > Is it normal memory that you simply have a special use-case for? > >> And the service alloc/free the memory based on the physical address, so if >> the service want to change the prot dynamically, vmalloc doesn't work, and >> fixmap is a little complex. > > Without further explanation of your use-case, this doesn't make sense to > me. I don't understand why the physical address matters -- that implies > you have other agents accessing this memory. If that's the case, I don't > see what changing the permissions buys you. > > Regardless, it sounds like either we're missing some infrastructure, or > you are mis-using existing APIs. > >> I think if I create the spacial memory in 4kb, then the service could >> use set_memory_ro() directly, right? > > Perhaps. If it's a vmalloc'd area, then yes (once Ard's patch to allow > that is in). I have more general concerns with your approach, in that I > still do not understand the problem you are trying to solve. >
Hi Mark,
Thanks for your reply. Maybe I didn't express it clearly, sorry for it.
The abstract process is the following: 1. do not create a large block, use 4kb for all of the memory(regardless of performance). setup_arch->paging_init()->map_mem()->__map_memblock()->create_mapping() 2. alloc a page and get the the linear mapping address. 3. modify judgment condition of the function set_memory_ro(), so it could handle the linear mapping range. 4. use set_memory_ro() to change the prot flag of the page which we get in step 2.
Is it safe?
Thanks, Xishi Qiu
> Thanks, > Mark. > > . >
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