Le 13/05/2023 à 15:25, Lorenzo Stoakes a écrit : > On Tue, May 09, 2023 at 02:12:41PM -0700, Lorenzo Stoakes wrote: >> On Tue, May 09, 2023 at 01:46:09PM -0700, Christoph Hellwig wrote: >>> On Tue, May 09, 2023 at 12:56:32PM -0400, Kent Overstreet wrote: >>>> From: Kent Overstreet <kent.overstreet@xxxxxxxxx> >>>> >>>> This is needed for bcachefs, which dynamically generates per-btree node >>>> unpack functions. >>> >>> No, we will never add back a way for random code allocating executable >>> memory in kernel space. >> >> Yeah I think I glossed over this aspect a bit as it looks ostensibly like simply >> reinstating a helper function because the code is now used in more than one >> place (at lsf/mm so a little distracted :) >> >> But it being exported is a problem. Perhaps there's another way of acheving the >> same aim without having to do so? > > Just to be abundantly clear, my original ack was a mistake (I overlooked > the _exporting_ of the function being as significant as it is and assumed > in an LSF/MM haze that it was simply a refactoring of _already available_ > functionality rather than newly providing a means to allocate directly > executable kernel memory). > > Exporting this is horrible for the numerous reasons expounded on in this > thread, we need a different solution. > > Nacked-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx> > I addition to that, I still don't understand why you bring back vmalloc_exec() instead of using module_alloc(). As reminded in a previous response, some architectures like powerpc/32s cannot allocate exec memory in vmalloc space. On powerpc this is because exec protection is performed on 256Mbytes segments and vmalloc space is flagged non-exec. Some other architectures have a constraint on distance between kernel core text and other text. Today you have for instance kprobes in the kernel that need dynamic exec memory. It uses module_alloc() to get it. On some architectures you also have ftrace that gets some exec memory with module_alloc(). So, I still don't understand why you cannot use module_alloc() and need vmalloc_exec() instead. Thanks Christophe
