Re: [PATCH 04/12] __wr_after_init: x86_64: __wr_op

From: Igor Stoppa
Date: Fri Dec 21 2018 - 12:42:34 EST

On 21/12/2018 19:23, Andy Lutomirski wrote:
On Thu, Dec 20, 2018 at 11:19 AM Igor Stoppa <igor.stoppa@xxxxxxxxx> wrote:

On 20/12/2018 20:49, Matthew Wilcox wrote:

I think you're causing yourself more headaches by implementing this "op"

I probably misinterpreted the initial criticism on my first patchset,
about duplication. Somehow, I'm still thinking to the endgame of having
higher-level functions, like list management.

Here's some generic code:

thank you, I have one question, below

void *wr_memcpy(void *dst, void *src, unsigned int len)
wr_state_t wr_state;
void *wr_poking_addr = __wr_addr(dst);

__wr_memcpy(wr_poking_addr, src, len);

Is __wraddr() invoked inside wm_memcpy() instead of being invoked
privately within __wr_memcpy() because the code is generic, or is there
some other reason?


return dst;

Now, x86 can define appropriate macros and functions to use the temporary_mm
functionality, and other architectures can do what makes sense to them.

I suspect that most architectures will want to do this exactly like
x86, though, but sure, it could be restructured like this.

In spirit, I think yes, but already I couldn't find a clean ways to do multi-arch wr_enable(&wr_state), so I made that too become arch_dependent.

Maybe after implementing write rare for a few archs, it becomes more clear (to me, any advice is welcome) which parts can be considered common.

On x86, I *think* that __wr_memcpy() will want to special-case len ==
1, 2, 4, and (on 64-bit) 8 byte writes to keep them atomic. i'm
guessing this is the same on most or all architectures.

I switched to xxx_user() approach, as you suggested.
For x86_64 I'm using copy_user() and i added a memset_user(), based on copy_user().

It's already assembly code optimized for dealing with multiples of 8-byte words or subsets. You can see this in the first patch of the patchset, even this one.

I'll send out the v3 patchset in a short while.