Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag

[Matthew Wilcox]

On Fri, Sep 18, 2020 at 02:45:25PM +0200, Christoph Hellwig wrote:
> Add a flag to force processing a syscall as a compat syscall.  This is
> required so that in_compat_syscall() works for I/O submitted by io_uring
> helper threads on behalf of compat syscalls.

Al doesn't like this much, but my suggestion is to introduce two new
opcodes -- IORING_OP_READV32 and IORING_OP_WRITEV32.  The compat code
can translate IORING_OP_READV to IORING_OP_READV32 and then the core
code can know what that user pointer is pointing to.