Re: [PATCH] revert "x86/mm: re-implement get_page_light() using an atomic increment"

["Roger Pau Monné" <roger.pau@citrix.com>]

On Mon, Apr 29, 2024 at 03:01:00PM +0200, Jan Beulich wrote:
> revert "x86/mm: re-implement get_page_light() using an atomic increment"
> 
> This reverts commit c40bc0576dcc5acd4d7e22ef628eb4642f568533.
> 
> That change aimed at eliminating an open-coded lock-like construct,
> which really isn't all that similar to, in particular, get_page(). The
> function always succeeds. Any remaining concern would want taking care
> of by placing block_lock_speculation() at the end of the function.
> Since the function is called only during page (de)validation, any
> possible performance concerns over such extra serialization could
> likely be addressed by pre-validating (e.g. via pinning) page tables.
> 
> The fundamental issue with the change being reverted is that it detects
> bad state only after already having caused possible corruption. While
> the system is going to be halted in such an event, there is a time
> window during which the resulting incorrect state could be leveraged by
> a clever (in particular: fast enough) attacker.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Acked-by: Roger Pau Monné <roger.pau@citrix.com>

Thanks.