linux-kernel - Re: [PATCH v4 3/8] x86/mm: Use 'ptdesc' when freeing PMD pages

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Message-ID: <20250905182559.GO616306@nvidia.com>
Date: Fri, 5 Sep 2025 15:25:59 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Lu Baolu <baolu.lu@...ux.intel.com>
Cc: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>,
	Kevin Tian <kevin.tian@...el.com>, Jann Horn <jannh@...gle.com>,
	Vasant Hegde <vasant.hegde@....com>,
	Dave Hansen <dave.hansen@...el.com>,
	Alistair Popple <apopple@...dia.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Jean-Philippe Brucker <jean-philippe@...aro.org>,
	Andy Lutomirski <luto@...nel.org>, Yi Lai <yi1.lai@...el.com>,
	iommu@...ts.linux.dev, security@...nel.org,
	linux-kernel@...r.kernel.org,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v4 3/8] x86/mm: Use 'ptdesc' when freeing PMD pages

On Fri, Sep 05, 2025 at 01:50:58PM +0800, Lu Baolu wrote:
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> There are a billion ways to refer to a physical memory address.
> One of the x86 PMD freeing code location chooses to use a 'pte_t *' to
> point to a PMD page and then call a PTE-specific freeing function for
> it.  That's a bit wonky.
> 
> Just use a 'struct ptdesc *' instead. Its entire purpose is to refer
> to page table pages. It also means being able to remove an explicit
> cast.
> 
> Right now, pte_free_kernel() is a one-liner that calls
> pagetable_dtor_free(). Effectively, all this patch does is
> remove one superfluous __pa(__va(paddr)) conversion and then
> call pagetable_dtor_free() directly instead of through a helper.
> 
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
>  arch/x86/mm/pgtable.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)

Much better

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason