Messages in this thread | | | Date | Tue, 7 May 2019 08:47:53 -0700 | From | Christoph Hellwig <> | Subject | Re: [PATCH RFC] vhost: don't use kmap() to log dirty pages |
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On Mon, May 06, 2019 at 10:23:29PM -0400, Jason Wang wrote: > Note: there're archs (few non popular ones) that don't implement > futex helper, we can't log dirty pages. We can fix them on top or > simply disable LOG_ALL features of vhost.
That means vhost now has to depend on HAVE_FUTEX_CMPXCHG to make sure we have a working implementation.
> #include <linux/sched/signal.h> > #include <linux/interval_tree_generic.h> > #include <linux/nospec.h> > +#include <asm/futex.h>
Also please include the futex maintainers to make sure they are fine with this first usage of <asm/futex.h> outside of kernel/futex.c.
> +static int set_bit_to_user(int nr, u32 __user *addr) > { > unsigned long log = (unsigned long)addr; > struct page *page; > + u32 old_log; > int r; > > r = get_user_pages_fast(log, 1, 1, &page); > if (r < 0) > return r; > BUG_ON(r != 1); > + > + r = futex_atomic_cmpxchg_inatomic(&old_log, addr, 0, 0); > + if (r < 0) > + return r; > + > + old_log |= 1 << nr; > + r = put_user(old_log, addr); > + if (r < 0) > + return r;
And this just looks odd to me. Why do we need the futex call to replace a 0 value with 0? Why does it still duplicate the put_user? This doesn't look like actually working code to me.
Also don't we need a pagefault_disable() around futex_atomic_cmpxchg_inatomic?
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