linux-kernel - Re: [PATCH v6 7/8] execmem: add support for cache of large ROX pages

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Message-ID: <ZxQ2saulzeSkUsEh@bombadil.infradead.org>
Date: Sat, 19 Oct 2024 15:46:09 -0700
From: Luis Chamberlain <mcgrof@...nel.org>
To: Mike Rapoport <rppt@...nel.org>
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Subject: Re: [PATCH v6 7/8] execmem: add support for cache of large ROX pages

On Wed, Oct 16, 2024 at 03:24:23PM +0300, Mike Rapoport wrote:
> From: "Mike Rapoport (Microsoft)" <rppt@...nel.org>
> 
> Using large pages to map text areas reduces iTLB pressure and improves
> performance.
> 
> Extend execmem_alloc() with an ability to use huge pages with ROX
> permissions as a cache for smaller allocations.
> 
> To populate the cache, a writable large page is allocated from vmalloc with
> VM_ALLOW_HUGE_VMAP, filled with invalid instructions and then remapped as
> ROX.
> 
> The direct map alias of that large page is exculded from the direct map.
> 
> Portions of that large page are handed out to execmem_alloc() callers
> without any changes to the permissions.
> 
> When the memory is freed with execmem_free() it is invalidated again so
> that it won't contain stale instructions.
> 
> An architecture has to implement execmem_fill_trapping_insns() callback
> and select ARCH_HAS_EXECMEM_ROX configuration option to be able to use
> the ROX cache.
> 
> The cache is enabled on per-range basis when an architecture sets
> EXECMEM_ROX_CACHE flag in definition of an execmem_range.
> 
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>

Reviewed-by: Luis Chamberlain <mcgrof@...nel.org>

  Luis