Re: [PATCH 0/5] x86/mm/pat: CPA fixes

[Mike Rapoport <rppt@kernel.org>]

@Dave, @Peter, how do you want to proceed with these?

On Tue, Jul 28, 2026 at 04:07:43PM +0300, Mike Rapoport (Microsoft) wrote:
> There are a couple of CPA fixes floating around:
> 
> Denis Lunev fixed races between split and collapse of the large mappings:
> 
> https://lore.kernel.org/all/20260715183453.2381141-1-den@openvz.org
> 
> Lorenzo Stoakes fixed UAF caused by races between CPA and ptdump:
> 
> https://lore.kernel.org/all/20260723-series-vmap-race-fix-v6-0-8cc77dcc0018@kernel.org
> 
> and an issue with stale page tables in IOMMU:
> 
> https://lore.kernel.org/all/20260721-fix-cpa-kernel-pagetables-v2-1-2b255deed710@kernel.org
> 
> Mike Rapoport fixed a check of RW attribute in lookup_address_in_pgd_attr()
> used for the verification of RWX:
> 
> https://lore.kernel.org/all/20260715144519.934289-1-rppt@kernel.org
> 
> Some of the fixes got merged into x86 tree, some of them got merged into mm
> tree and some are still hanging in the air.
> 
> Beside the fixes there was a supposed simplification of cpa_lock locking 
> that looked like removal of an optimization for DEBUG_PAGEALLOC, but it
> turned out that it was not an optimization but rather a correctness
> guard because with DEBUG_PAGEALLOC the locks could be taken in an atomic
> context and couldn't use plain spin_lock()/spin_unlock().
> 
> The changes here are collected from all these fixes into a sinlge coherent
> set on top of tip/x86/mm:
>  
> * update to cpa_lock handling with DEBUG_PAGEALLOC
> * fix for races between CPA and ptdumpi causing UAF
> * fix for stale page tables in IOMMU
> * update to the fix of the race between split and collapse of large
>   mappings
> * fix for effective RW computation in lookup_address_in_pgd_attr()
> 
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
> Lorenzo Stoakes (ARM) (3):
>       x86/mm/pat: acquire init_mm write lock on collapse to avoid UAF
>       x86/mm/pat: acquire init_mm read lock on attribute change to avoid UAF
>       x86/mm/pat: allocate split page tables as kernel page tables
> 
> Mike Rapoport (Microsoft) (2):
>       x86/mm/pat: introcude cpa_lock() and cpa_unlock()
>       x86/mm/pat: fix effective RW computation in lookup_address_in_pgd_attr()
> 
>  arch/x86/mm/pat/set_memory.c | 95 +++++++++++++++++++++++++++++++-------------
>  include/linux/mmap_lock.h    |  2 +
>  2 files changed, 70 insertions(+), 27 deletions(-)
> ---
> base-commit: a5a162fe1ae130e3d2ceefef3f43afe3773c1d56
> change-id: 20260727-cpa-fixes-d3c73c075672
> 
> --
> Sincerely yours,
> Mike.
> 

-- 
Sincerely yours,
Mike.