Re: [PATCH 2/2] x86/modules: Make x86 allocs to flush when free

[Andy Lutomirski]

> On Nov 27, 2018, at 4:07 PM, Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx> wrote:
>
> Change the module allocations to flush before freeing the pages.
>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> ---
> arch/x86/kernel/module.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
> index b052e883dd8c..1694daf256b3 100644
> --- a/arch/x86/kernel/module.c
> +++ b/arch/x86/kernel/module.c
> @@ -87,8 +87,8 @@ void *module_alloc(unsigned long size)
>    p = __vmalloc_node_range(size, MODULE_ALIGN,
>                    MODULES_VADDR + get_module_load_offset(),
>                    MODULES_END, GFP_KERNEL,
> -                    PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE,
> -                    __builtin_return_address(0));
> +                    PAGE_KERNEL_EXEC, VM_IMMEDIATE_UNMAP,
> +                    NUMA_NO_NODE, __builtin_return_address(0));

Hmm. How awful is the resulting performance for heavy eBPF users?  Iâm
wondering if the JIT will need some kind of cache to reuse
allocations.

>    if (p && (kasan_module_alloc(p, size) < 0)) {
>        vfree(p);
>        return NULL;
> --
> 2.17.1
>