On 5/12/21 12:54 AM, Joerg Roedel wrote:

The put_user() and get_user() functions do checks on the address which is
passed to them. They check whether the address is actually a user-space
address and whether its fine to access it. They also call might_fault()
to indicate that they could fault and possibly sleep.

All of these checks are neither wanted nor required in the #VC exception
handler, which can be invoked from almost any context and also for MMIO
instructions from kernel space on kernel memory. All the #VC handler
wants to know is whether a fault happened when the access was tried.

This is provided by __put_user()/__get_user(), which just do the access
no matter what.

The changelog _helps_, but using a "user" function to handle kernel MMIO
for its error handling properties seems like it's begging for a comment.

__put_user() also seems to have fun stuff like __chk_user_ptr().  It all
seems sketchy to me.
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