[PATCH v6 0/4] Convert x86/mm/pat to generic page table apis

[PATCH v6 0/4] Convert x86/mm/pat to generic page table apis

[Vishal Moola (Oracle)]

set_memory.c has a call to pagetable_free(), while the allocation sites
use get_free_pages(). This causes issues separately allocating ptdescs
from struct page.

It turns out that we can just use the appropriate generic pagetable
apis for allocation/freeing. This helps simplify and standardize the
code.

In the short term, this helps enable Matthew's work to allocate frozen
pagetables[1]. And in the long term, this will help us cleanly split
ptdesc allocations from struct page[2].

[1] https://lore.kernel.org/linux-mm/20251113140448.1814860-1-willy@infradead.org/
[2] https://lore.kernel.org/linux-mm/20251020001652.2116669-1-willy@infradead.org/

------

Based on current mm-new.

v6:
  - Drop the renaming of *page* functions
  - Use existing page table api instead of creating new apis
  - Split the pmd and populate_pgd() changes into separate patches
  - Reword the cover letter to describe the new approach

v5 link: 
https://lore.kernel.org/all/20260211195233.368497-1-vishal.moola@gmail.com/

Vishal Moola (Oracle) (4):
  x86/mm/pat: Convert pte code to use page table apis
  x86/mm/pat: Convert pmd code to use page table apis
  x86/mm/pat: Convert populate_pgd() to use page table apis
  x86/mm/pat: Convert split_large_page() to use ptdescs

 arch/x86/mm/pat/set_memory.c | 36 ++++++++++++++++++++++++------------
 1 file changed, 24 insertions(+), 12 deletions(-)

-- 
2.53.0

[PATCH v6 1/4] x86/mm/pat: Convert pte code to use page table apis

[Vishal Moola (Oracle)]

We need all allocation and free sites to use the ptdesc APIs in order to
allocate them separately from regular pages. Convert the pte
allocation/free sites to use the generic page table apis, since those
use ptdescs already.

Pass through init_mm since these are kernel page tables,
pte_alloc_one_kernel() effectively becomes a no-op otherwise.

Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
---
 arch/x86/mm/pat/set_memory.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 6c6eb486f7a6..d52010fd3023 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -1408,7 +1408,7 @@ static bool try_to_free_pte_page(pte_t *pte)
 		if (!pte_none(pte[i]))
 			return false;
 
-	free_page((unsigned long)pte);
+	pte_free_kernel(&init_mm, pte);
 	return true;
 }
 
@@ -1539,7 +1539,7 @@ static void unmap_pud_range(p4d_t *p4d, unsigned long start, unsigned long end)
 
 static int alloc_pte_page(pmd_t *pmd)
 {
-	pte_t *pte = (pte_t *)get_zeroed_page(GFP_KERNEL);
+	pte_t *pte = pte_alloc_one_kernel(&init_mm);
 	if (!pte)
 		return -1;
 
-- 
2.53.0

[PATCH v6 2/4] x86/mm/pat: Convert pmd code to use page table apis

[Vishal Moola (Oracle)]

We need all allocation and free sites to use the ptdesc APIs in order to
allocate them separately from regular pages. Convert the pmd
allocation/free sites to use the generic page table apis, since those
use ptdescs already.

Pass through init_mm since these are kernel page tables, pmd_alloc_one()
needs it to identify kernel page tables. Also, the generic implementation
doesn't use the second argument. Pass it a placeholder so we don't have
to reimplement it or risk breaking other architectures.

Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
---
 arch/x86/mm/pat/set_memory.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index d52010fd3023..655bef618ea0 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -1420,7 +1420,7 @@ static bool try_to_free_pmd_page(pmd_t *pmd)
 		if (!pmd_none(pmd[i]))
 			return false;
 
-	free_page((unsigned long)pmd);
+	pmd_free(&init_mm, pmd);
 	return true;
 }
 
@@ -1549,7 +1549,10 @@ static int alloc_pte_page(pmd_t *pmd)
 
 static int alloc_pmd_page(pud_t *pud)
 {
-	pmd_t *pmd = (pmd_t *)get_zeroed_page(GFP_KERNEL);
+	/* The generic implementation of pmd_alloc_one() doesn't use
+	 * the second argument. Pass it 0 as a placeholder.
+	 */
+	pmd_t *pmd = pmd_alloc_one(&init_mm, 0);
 	if (!pmd)
 		return -1;
 
-- 
2.53.0

[PATCH v6 3/4] x86/mm/pat: Convert populate_pgd() to use page table apis

[Vishal Moola (Oracle)]

We need all allocation and free sites to use the ptdesc APIs in order to
allocate them separately from regular pages. Convert the remaining
get_zeroed_page() calls to the generic page table apis, since those
use ptdescs already.

Pass through init_mm since these are kernel page tables, both functions
need it to identify kernel page tables. Also, the generic
implementations don't use the second argument. Pass it a placeholder so
we don't have to reimplement it or risk breaking other architectures.

Its not obvious if these pages get freed. Regardless, the only other
possible free paths have already been converted, and my frozen page
table test kernel hasn't found any issues.

Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
---
 arch/x86/mm/pat/set_memory.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 655bef618ea0..8f74d4bfd591 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -1746,7 +1746,11 @@ static int populate_pgd(struct cpa_data *cpa, unsigned long addr)
 	pgd_entry = cpa->pgd + pgd_index(addr);
 
 	if (pgd_none(*pgd_entry)) {
-		p4d = (p4d_t *)get_zeroed_page(GFP_KERNEL);
+		/* The generic implementation of p4d_alloc_one()
+		 * doesn't use the second argument. Pass it 0 as
+		 * a placeholder.
+		 */
+		p4d = p4d_alloc_one(&init_mm, 0);
 		if (!p4d)
 			return -1;
 
@@ -1758,7 +1762,11 @@ static int populate_pgd(struct cpa_data *cpa, unsigned long addr)
 	 */
 	p4d = p4d_offset(pgd_entry, addr);
 	if (p4d_none(*p4d)) {
-		pud = (pud_t *)get_zeroed_page(GFP_KERNEL);
+		/* The generic implementation of pud_alloc_one()
+		 * doesn't use the second argument. Pass it 0 as
+		 * a placeholder.
+		 */
+		pud = pud_alloc_one(&init_mm, 0);
 		if (!pud)
 			return -1;
 
-- 
2.53.0

[PATCH v6 4/4] x86/mm/pat: Convert split_large_page() to use ptdescs

[Vishal Moola (Oracle)]

In order to separately allocate ptdescs from pages, we need all allocation
and free sites to use the appropriate functions.

split_large_page() allocates a page to be used as a page table. This
should be allocating a ptdesc, so convert it.

Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 arch/x86/mm/pat/set_memory.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 8f74d4bfd591..e26535f3b8bd 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -1119,9 +1119,10 @@ static void split_set_pte(struct cpa_data *cpa, pte_t *pte, unsigned long pfn,
 
 static int
 __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
-		   struct page *base)
+		   struct ptdesc *ptdesc)
 {
 	unsigned long lpaddr, lpinc, ref_pfn, pfn, pfninc = 1;
+	struct page *base = ptdesc_page(ptdesc);
 	pte_t *pbase = (pte_t *)page_address(base);
 	unsigned int i, level;
 	pgprot_t ref_prot;
@@ -1226,18 +1227,18 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
 static int split_large_page(struct cpa_data *cpa, pte_t *kpte,
 			    unsigned long address)
 {
-	struct page *base;
+	struct ptdesc *ptdesc;
 
 	if (!debug_pagealloc_enabled())
 		spin_unlock(&cpa_lock);
-	base = alloc_pages(GFP_KERNEL, 0);
+	ptdesc = pagetable_alloc(GFP_KERNEL, 0);
 	if (!debug_pagealloc_enabled())
 		spin_lock(&cpa_lock);
-	if (!base)
+	if (!ptdesc)
 		return -ENOMEM;
 
-	if (__split_large_page(cpa, kpte, address, base))
-		__free_page(base);
+	if (__split_large_page(cpa, kpte, address, ptdesc))
+		pagetable_free(ptdesc);
 
 	return 0;
 }
-- 
2.53.0

Re: [PATCH v6 0/4] Convert x86/mm/pat to generic page table apis

[Mike Rapoport]

On Wed, Feb 18, 2026 at 06:03:50PM -0800, Vishal Moola (Oracle) wrote:
> set_memory.c has a call to pagetable_free(), while the allocation sites
> use get_free_pages(). This causes issues separately allocating ptdescs
> from struct page.
> 
> It turns out that we can just use the appropriate generic pagetable
> apis for allocation/freeing. This helps simplify and standardize the
> code.
> 
> In the short term, this helps enable Matthew's work to allocate frozen
> pagetables[1]. And in the long term, this will help us cleanly split
> ptdesc allocations from struct page[2].
> 
> [1] https://lore.kernel.org/linux-mm/20251113140448.1814860-1-willy@infradead.org/
> [2] https://lore.kernel.org/linux-mm/20251020001652.2116669-1-willy@infradead.org/
> 
> ------
> 
> Based on current mm-new.
> 
> v6:
>   - Drop the renaming of *page* functions
>   - Use existing page table api instead of creating new apis
>   - Split the pmd and populate_pgd() changes into separate patches
>   - Reword the cover letter to describe the new approach
> 
> v5 link: 
> https://lore.kernel.org/all/20260211195233.368497-1-vishal.moola@gmail.com/
> 
> Vishal Moola (Oracle) (4):
>   x86/mm/pat: Convert pte code to use page table apis
>   x86/mm/pat: Convert pmd code to use page table apis
>   x86/mm/pat: Convert populate_pgd() to use page table apis
>   x86/mm/pat: Convert split_large_page() to use ptdescs
> 
>  arch/x86/mm/pat/set_memory.c | 36 ++++++++++++++++++++++++------------
>  1 file changed, 24 insertions(+), 12 deletions(-)

Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

> 
> -- 
> 2.53.0
> 

-- 
Sincerely yours,
Mike.

Re: [PATCH v6 0/4] Convert x86/mm/pat to generic page table apis

[Vishal Moola (Oracle)]

On Wed, Feb 18, 2026 at 06:03:50PM -0800, Vishal Moola (Oracle) wrote:
> set_memory.c has a call to pagetable_free(), while the allocation sites
> use get_free_pages(). This causes issues separately allocating ptdescs
> from struct page.
> 
> It turns out that we can just use the appropriate generic pagetable
> apis for allocation/freeing. This helps simplify and standardize the
> code.
> 
> In the short term, this helps enable Matthew's work to allocate frozen
> pagetables[1]. And in the long term, this will help us cleanly split
> ptdesc allocations from struct page[2].
> 
> [1] https://lore.kernel.org/linux-mm/20251113140448.1814860-1-willy@infradead.org/
> [2] https://lore.kernel.org/linux-mm/20251020001652.2116669-1-willy@infradead.org/
> 
> ------
>
> Based on current mm-new.

Hi Dave,

Do you have any more comments for this series? If not, could you please
take this through the x86 tree. Thanks :)

> v6:
>   - Drop the renaming of *page* functions
>   - Use existing page table api instead of creating new apis
>   - Split the pmd and populate_pgd() changes into separate patches
>   - Reword the cover letter to describe the new approach
> 
> v5 link: 
> https://lore.kernel.org/all/20260211195233.368497-1-vishal.moola@gmail.com/
> 
> Vishal Moola (Oracle) (4):
>   x86/mm/pat: Convert pte code to use page table apis
>   x86/mm/pat: Convert pmd code to use page table apis
>   x86/mm/pat: Convert populate_pgd() to use page table apis
>   x86/mm/pat: Convert split_large_page() to use ptdescs
> 
>  arch/x86/mm/pat/set_memory.c | 36 ++++++++++++++++++++++++------------
>  1 file changed, 24 insertions(+), 12 deletions(-)
> 
> -- 
> 2.53.0
> 

Re: [PATCH v6 0/4] Convert x86/mm/pat to generic page table apis

[Dave Hansen]

On 2/27/26 12:07, Vishal Moola (Oracle) wrote:
> Do you have any more comments for this series? If not, could you please
> take this through the x86 tree. Thanks 🙂

From a 2-second glance, this doesn't have normal comment style and isn't
using imperative voice. Quite a few "we's". Looks like it needs some
more eyeballs.

Re: [PATCH v6 0/4] Convert x86/mm/pat to generic page table apis

[Vishal Moola (Oracle)]

On Fri, Feb 27, 2026 at 02:24:33PM -0800, Dave Hansen wrote:
> On 2/27/26 12:07, Vishal Moola (Oracle) wrote:
> > Do you have any more comments for this series? If not, could you please
> > take this through the x86 tree. Thanks 🙂
> 
> From a 2-second glance, this doesn't have normal comment style and isn't
> using imperative voice. Quite a few "we's". Looks like it needs some
> more eyeballs.

Ok, my mistake on the comment style. I'll fix that.

Sorry I'm not the greatest at imperative voice, I'll pass all my comments
through AI to convert them all to imperative voice.

In regards to more eyeballs, I've realized I didn't cc ALL x86
maintainers. +CC the rest of the x86 maintainers and we'll hope
someone else looks at it as well.

Re: [PATCH v6 0/4] Convert x86/mm/pat to generic page table apis

[Dave Hansen]

On 2/27/26 16:44, Vishal Moola (Oracle) wrote:
> On Fri, Feb 27, 2026 at 02:24:33PM -0800, Dave Hansen wrote:
>> On 2/27/26 12:07, Vishal Moola (Oracle) wrote:
>>> Do you have any more comments for this series? If not, could you please
>>> take this through the x86 tree. Thanks 🙂
>>
>> From a 2-second glance, this doesn't have normal comment style and isn't
>> using imperative voice. Quite a few "we's". Looks like it needs some
>> more eyeballs.
> 
> Ok, my mistake on the comment style. I'll fix that.
> 
> Sorry I'm not the greatest at imperative voice, I'll pass all my comments
> through AI to convert them all to imperative voice.
> 
> In regards to more eyeballs, I've realized I didn't cc ALL x86
> maintainers. +CC the rest of the x86 maintainers and we'll hope
> someone else looks at it as well.

I was actually kinda hoping you'd be able to actively go out and find
some reviewers other than the maintainers.

Re: [PATCH v6 0/4] Convert x86/mm/pat to generic page table apis

[Vishal Moola (Oracle)]

On Mon, Mar 02, 2026 at 09:33:31AM -0800, Dave Hansen wrote:
> On 2/27/26 16:44, Vishal Moola (Oracle) wrote:
> > On Fri, Feb 27, 2026 at 02:24:33PM -0800, Dave Hansen wrote:
> >> On 2/27/26 12:07, Vishal Moola (Oracle) wrote:
> >>> Do you have any more comments for this series? If not, could you please
> >>> take this through the x86 tree. Thanks 🙂
> >>
> >> From a 2-second glance, this doesn't have normal comment style and isn't
> >> using imperative voice. Quite a few "we's". Looks like it needs some
> >> more eyeballs.
> > 
> > Ok, my mistake on the comment style. I'll fix that.
> > 
> > Sorry I'm not the greatest at imperative voice, I'll pass all my comments
> > through AI to convert them all to imperative voice.
> > 
> > In regards to more eyeballs, I've realized I didn't cc ALL x86
> > maintainers. +CC the rest of the x86 maintainers and we'll hope
> > someone else looks at it as well.
> 
> I was actually kinda hoping you'd be able to actively go out and find
> some reviewers other than the maintainers.

I'd appreciate if you could give me more guidance on this. Who am I
supposed to go, if not the people from ./get_maintainers? I don't know
the x86 folks, I interact more with mm.

You've been giving valuable feedback to ensure the stylistic choices
meet your expectations. I have mentioned I'll have another version
*trying* to meet those stylistic expectations.

Mike has been very active in reviewing the ptdesc work (thanks!), and
he's provided valuable review about the code itself. I don't know about
you, but I trust his expertise on the topic of page tables.

So, I don't even know what you want from the "more eyeballs."
Do you want me to email a bunch of people unfamiliar with x86 and tell
them to catch what you (or any other specialized individual) would
catch? That doesn't sound productive *to me*.

This is on the x86 mailing list. And honestly, this current iteration is
simple enough that anyone specialized and interested could have taken a
look at it and to provide some feedback.

Please do let me know. I'd love to work with you not against you, but
that's difficult when you don't provide any guidance/pointers about the
issues you have with the patchset (or process?).

Re: [PATCH v6 0/4] Convert x86/mm/pat to generic page table apis

[Dave Hansen]

On 3/2/26 12:27, Vishal Moola (Oracle) wrote:
>> I was actually kinda hoping you'd be able to actively go out and find
>> some reviewers other than the maintainers.
> I'd appreciate if you could give me more guidance on this. Who am I
> supposed to go, if not the people from ./get_maintainers? I don't know
> the x86 folks, I interact more with mm.

Hi Vishal,

I personally look at 'git blame' or 'git log' manually and see who's
been mucking around in the file recently. get_maintainers.pl does _some_
of that, but I think it mostly looks at others who modified the sames
lines you did. That can be a bit too restrictive.

It also couldn't hurt to take a quick look at lore for who's been
patching the files that you are, or commenting in threads.

The more of that which you can manage to do this now is less of it that
I have to do later. Any effort in the area would be much appreciated!

Oh, and if you have a friendly LLM, it doesn't hurt to dump your patches
in there and ask it. Couldn't hurt.