[v5] fix wrong usage of memory allocation APIs under PREEMPT_RT in arm64

[PATCH v5 3/3] arm64: mmu: avoid allocating pages while installing ng-mapping for KPTI

Posted by Yeoreum Yun 1 month ago

The current __kpti_install_ng_mappings() allocates a temporary PGD
while installing the NG mapping for KPTI under stop_machine(),
using GFP_ATOMIC.

This is fine in the non-PREEMPT_RT case. However, it becomes a problem
under PREEMPT_RT because generic memory allocation/free APIs
(e.g., pgtable_alloc(), __get_free_pages(), etc.) cannot be invoked
in a non-preemptible context, except for the *_nolock() variants.
These generic allocators may sleep due to their use of spin_lock().

In other words, calling __get_free_pages(), even with GFP_ATOMIC,
is not allowed in __kpti_install_ng_mappings(), which is executed by
the stopper thread where preemption is disabled under PREEMPT_RT.

To address this, preallocate the page needed for the temporary PGD
before invoking __kpti_install_ng_mappings() via stop_machine().

Fixes: 47546a1912fc ("arm64: mm: install KPTI nG mappings with MMU enabled")
Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
---
 arch/arm64/mm/mmu.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 120874a2d35b..6ea5b80ab54f 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1360,7 +1360,7 @@ static phys_addr_t __init kpti_ng_pgd_alloc(enum pgtable_type type)
 	return kpti_ng_temp_alloc;
 }
 
-static int __init __kpti_install_ng_mappings(void *__unused)
+static int __init __kpti_install_ng_mappings(void *data)
 {
 	typedef void (kpti_remap_fn)(int, int, phys_addr_t, unsigned long);
 	extern kpti_remap_fn idmap_kpti_install_ng_mappings;
@@ -1368,10 +1368,9 @@ static int __init __kpti_install_ng_mappings(void *__unused)
 
 	int cpu = smp_processor_id();
 	int levels = CONFIG_PGTABLE_LEVELS;
-	int order = order_base_2(levels);
 	u64 kpti_ng_temp_pgd_pa = 0;
 	pgd_t *kpti_ng_temp_pgd;
-	u64 alloc = 0;
+	u64 alloc = *(u64 *)data;
 
 	if (levels == 5 && !pgtable_l5_enabled())
 		levels = 4;
@@ -1382,8 +1381,6 @@ static int __init __kpti_install_ng_mappings(void *__unused)
 
 	if (!cpu) {
 		int ret;
-
-		alloc = __get_free_pages(GFP_ATOMIC | __GFP_ZERO, order);
 		kpti_ng_temp_pgd = (pgd_t *)(alloc + (levels - 1) * PAGE_SIZE);
 		kpti_ng_temp_alloc = kpti_ng_temp_pgd_pa = __pa(kpti_ng_temp_pgd);
 
@@ -1414,16 +1411,16 @@ static int __init __kpti_install_ng_mappings(void *__unused)
 	remap_fn(cpu, num_online_cpus(), kpti_ng_temp_pgd_pa, KPTI_NG_TEMP_VA);
 	cpu_uninstall_idmap();
 
-	if (!cpu) {
-		free_pages(alloc, order);
+	if (!cpu)
 		arm64_use_ng_mappings = true;
-	}
 
 	return 0;
 }
 
 void __init kpti_install_ng_mappings(void)
 {
+	int order = order_base_2(CONFIG_PGTABLE_LEVELS);
+	u64 alloc;
 	/* Check whether KPTI is going to be used */
 	if (!arm64_kernel_unmapped_at_el0())
 		return;
@@ -1436,8 +1433,14 @@ void __init kpti_install_ng_mappings(void)
 	if (arm64_use_ng_mappings)
 		return;
 
+	alloc = __get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
+	if (!alloc)
+		panic("Failed to alloc page tables\n");
+
 	init_idmap_kpti_bbml2_flag();
-	stop_machine(__kpti_install_ng_mappings, NULL, cpu_online_mask);
+	stop_machine(__kpti_install_ng_mappings, &alloc, cpu_online_mask);
+
+	free_pages(alloc, order);
 }
 
 static pgprot_t __init kernel_exec_prot(void)
-- 
LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}

Re: [PATCH v5 3/3] arm64: mmu: avoid allocating pages while installing ng-mapping for KPTI

Posted by Will Deacon 3 weeks ago

On Mon, Jan 05, 2026 at 08:23:28PM +0000, Yeoreum Yun wrote:
> The current __kpti_install_ng_mappings() allocates a temporary PGD
> while installing the NG mapping for KPTI under stop_machine(),
> using GFP_ATOMIC.
> 
> This is fine in the non-PREEMPT_RT case. However, it becomes a problem
> under PREEMPT_RT because generic memory allocation/free APIs
> (e.g., pgtable_alloc(), __get_free_pages(), etc.) cannot be invoked
> in a non-preemptible context, except for the *_nolock() variants.
> These generic allocators may sleep due to their use of spin_lock().
> 
> In other words, calling __get_free_pages(), even with GFP_ATOMIC,
> is not allowed in __kpti_install_ng_mappings(), which is executed by
> the stopper thread where preemption is disabled under PREEMPT_RT.
> 
> To address this, preallocate the page needed for the temporary PGD
> before invoking __kpti_install_ng_mappings() via stop_machine().
> 
> Fixes: 47546a1912fc ("arm64: mm: install KPTI nG mappings with MMU enabled")
> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
> ---
>  arch/arm64/mm/mmu.c | 21 ++++++++++++---------
>  1 file changed, 12 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 120874a2d35b..6ea5b80ab54f 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1360,7 +1360,7 @@ static phys_addr_t __init kpti_ng_pgd_alloc(enum pgtable_type type)
>  	return kpti_ng_temp_alloc;
>  }
>  
> -static int __init __kpti_install_ng_mappings(void *__unused)
> +static int __init __kpti_install_ng_mappings(void *data)
>  {
>  	typedef void (kpti_remap_fn)(int, int, phys_addr_t, unsigned long);
>  	extern kpti_remap_fn idmap_kpti_install_ng_mappings;
> @@ -1368,10 +1368,9 @@ static int __init __kpti_install_ng_mappings(void *__unused)
>  
>  	int cpu = smp_processor_id();
>  	int levels = CONFIG_PGTABLE_LEVELS;
> -	int order = order_base_2(levels);
>  	u64 kpti_ng_temp_pgd_pa = 0;
>  	pgd_t *kpti_ng_temp_pgd;
> -	u64 alloc = 0;
> +	u64 alloc = *(u64 *)data;
>  
>  	if (levels == 5 && !pgtable_l5_enabled())
>  		levels = 4;
> @@ -1382,8 +1381,6 @@ static int __init __kpti_install_ng_mappings(void *__unused)
>  
>  	if (!cpu) {
>  		int ret;
> -
> -		alloc = __get_free_pages(GFP_ATOMIC | __GFP_ZERO, order);
>  		kpti_ng_temp_pgd = (pgd_t *)(alloc + (levels - 1) * PAGE_SIZE);
>  		kpti_ng_temp_alloc = kpti_ng_temp_pgd_pa = __pa(kpti_ng_temp_pgd);
>  
> @@ -1414,16 +1411,16 @@ static int __init __kpti_install_ng_mappings(void *__unused)
>  	remap_fn(cpu, num_online_cpus(), kpti_ng_temp_pgd_pa, KPTI_NG_TEMP_VA);
>  	cpu_uninstall_idmap();
>  
> -	if (!cpu) {
> -		free_pages(alloc, order);
> +	if (!cpu)
>  		arm64_use_ng_mappings = true;
> -	}
>  
>  	return 0;
>  }
>  
>  void __init kpti_install_ng_mappings(void)
>  {
> +	int order = order_base_2(CONFIG_PGTABLE_LEVELS);
> +	u64 alloc;
>  	/* Check whether KPTI is going to be used */
>  	if (!arm64_kernel_unmapped_at_el0())
>  		return;
> @@ -1436,8 +1433,14 @@ void __init kpti_install_ng_mappings(void)
>  	if (arm64_use_ng_mappings)
>  		return;
>  
> +	alloc = __get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
> +	if (!alloc)
> +		panic("Failed to alloc page tables\n");

Why are you adding this panic?

Will

Re: [PATCH v5 3/3] arm64: mmu: avoid allocating pages while installing ng-mapping for KPTI

Posted by Yeoreum Yun 2 weeks, 6 days ago

Hi Will,

> On Mon, Jan 05, 2026 at 08:23:28PM +0000, Yeoreum Yun wrote:
> > The current __kpti_install_ng_mappings() allocates a temporary PGD
> > while installing the NG mapping for KPTI under stop_machine(),
> > using GFP_ATOMIC.
> >
> > This is fine in the non-PREEMPT_RT case. However, it becomes a problem
> > under PREEMPT_RT because generic memory allocation/free APIs
> > (e.g., pgtable_alloc(), __get_free_pages(), etc.) cannot be invoked
> > in a non-preemptible context, except for the *_nolock() variants.
> > These generic allocators may sleep due to their use of spin_lock().
> >
> > In other words, calling __get_free_pages(), even with GFP_ATOMIC,
> > is not allowed in __kpti_install_ng_mappings(), which is executed by
> > the stopper thread where preemption is disabled under PREEMPT_RT.
> >
> > To address this, preallocate the page needed for the temporary PGD
> > before invoking __kpti_install_ng_mappings() via stop_machine().
> >
> > Fixes: 47546a1912fc ("arm64: mm: install KPTI nG mappings with MMU enabled")
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> > Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
> > ---
> >  arch/arm64/mm/mmu.c | 21 ++++++++++++---------
> >  1 file changed, 12 insertions(+), 9 deletions(-)
> >
> > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> > index 120874a2d35b..6ea5b80ab54f 100644
> > --- a/arch/arm64/mm/mmu.c
> > +++ b/arch/arm64/mm/mmu.c
> > @@ -1360,7 +1360,7 @@ static phys_addr_t __init kpti_ng_pgd_alloc(enum pgtable_type type)
> >  	return kpti_ng_temp_alloc;
> >  }
> >
> > -static int __init __kpti_install_ng_mappings(void *__unused)
> > +static int __init __kpti_install_ng_mappings(void *data)
> >  {
> >  	typedef void (kpti_remap_fn)(int, int, phys_addr_t, unsigned long);
> >  	extern kpti_remap_fn idmap_kpti_install_ng_mappings;
> > @@ -1368,10 +1368,9 @@ static int __init __kpti_install_ng_mappings(void *__unused)
> >
> >  	int cpu = smp_processor_id();
> >  	int levels = CONFIG_PGTABLE_LEVELS;
> > -	int order = order_base_2(levels);
> >  	u64 kpti_ng_temp_pgd_pa = 0;
> >  	pgd_t *kpti_ng_temp_pgd;
> > -	u64 alloc = 0;
> > +	u64 alloc = *(u64 *)data;
> >
> >  	if (levels == 5 && !pgtable_l5_enabled())
> >  		levels = 4;
> > @@ -1382,8 +1381,6 @@ static int __init __kpti_install_ng_mappings(void *__unused)
> >
> >  	if (!cpu) {
> >  		int ret;
> > -
> > -		alloc = __get_free_pages(GFP_ATOMIC | __GFP_ZERO, order);
> >  		kpti_ng_temp_pgd = (pgd_t *)(alloc + (levels - 1) * PAGE_SIZE);
> >  		kpti_ng_temp_alloc = kpti_ng_temp_pgd_pa = __pa(kpti_ng_temp_pgd);
> >
> > @@ -1414,16 +1411,16 @@ static int __init __kpti_install_ng_mappings(void *__unused)
> >  	remap_fn(cpu, num_online_cpus(), kpti_ng_temp_pgd_pa, KPTI_NG_TEMP_VA);
> >  	cpu_uninstall_idmap();
> >
> > -	if (!cpu) {
> > -		free_pages(alloc, order);
> > +	if (!cpu)
> >  		arm64_use_ng_mappings = true;
> > -	}
> >
> >  	return 0;
> >  }
> >
> >  void __init kpti_install_ng_mappings(void)
> >  {
> > +	int order = order_base_2(CONFIG_PGTABLE_LEVELS);
> > +	u64 alloc;
> >  	/* Check whether KPTI is going to be used */
> >  	if (!arm64_kernel_unmapped_at_el0())
> >  		return;
> > @@ -1436,8 +1433,14 @@ void __init kpti_install_ng_mappings(void)
> >  	if (arm64_use_ng_mappings)
> >  		return;
> >
> > +	alloc = __get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
> > +	if (!alloc)
> > +		panic("Failed to alloc page tables\n");
>
> Why are you adding this panic?

Because original code call the panic() when it fails to create
mapping of kpti_ng_temp_pgd and I think allocation is also part
of creating kpti_ng_temp_pgd too.
So, I added this panic() when allocation is failed for kpti_ng_temp_pgd.

--
Sincerely,
Yeoreum Yun

Re: [PATCH v5 3/3] arm64: mmu: avoid allocating pages while installing ng-mapping for KPTI

Posted by Will Deacon 2 weeks, 6 days ago

On Mon, Jan 19, 2026 at 09:30:30PM +0000, Yeoreum Yun wrote:
> Hi Will,
> 
> > On Mon, Jan 05, 2026 at 08:23:28PM +0000, Yeoreum Yun wrote:
> > > The current __kpti_install_ng_mappings() allocates a temporary PGD
> > > while installing the NG mapping for KPTI under stop_machine(),
> > > using GFP_ATOMIC.
> > >
> > > This is fine in the non-PREEMPT_RT case. However, it becomes a problem
> > > under PREEMPT_RT because generic memory allocation/free APIs
> > > (e.g., pgtable_alloc(), __get_free_pages(), etc.) cannot be invoked
> > > in a non-preemptible context, except for the *_nolock() variants.
> > > These generic allocators may sleep due to their use of spin_lock().
> > >
> > > In other words, calling __get_free_pages(), even with GFP_ATOMIC,
> > > is not allowed in __kpti_install_ng_mappings(), which is executed by
> > > the stopper thread where preemption is disabled under PREEMPT_RT.
> > >
> > > To address this, preallocate the page needed for the temporary PGD
> > > before invoking __kpti_install_ng_mappings() via stop_machine().
> > >
> > > Fixes: 47546a1912fc ("arm64: mm: install KPTI nG mappings with MMU enabled")
> > > Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> > > Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
> > > ---
> > >  arch/arm64/mm/mmu.c | 21 ++++++++++++---------
> > >  1 file changed, 12 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> > > index 120874a2d35b..6ea5b80ab54f 100644
> > > --- a/arch/arm64/mm/mmu.c
> > > +++ b/arch/arm64/mm/mmu.c
> > > @@ -1360,7 +1360,7 @@ static phys_addr_t __init kpti_ng_pgd_alloc(enum pgtable_type type)
> > >  	return kpti_ng_temp_alloc;
> > >  }
> > >
> > > -static int __init __kpti_install_ng_mappings(void *__unused)
> > > +static int __init __kpti_install_ng_mappings(void *data)
> > >  {
> > >  	typedef void (kpti_remap_fn)(int, int, phys_addr_t, unsigned long);
> > >  	extern kpti_remap_fn idmap_kpti_install_ng_mappings;
> > > @@ -1368,10 +1368,9 @@ static int __init __kpti_install_ng_mappings(void *__unused)
> > >
> > >  	int cpu = smp_processor_id();
> > >  	int levels = CONFIG_PGTABLE_LEVELS;
> > > -	int order = order_base_2(levels);
> > >  	u64 kpti_ng_temp_pgd_pa = 0;
> > >  	pgd_t *kpti_ng_temp_pgd;
> > > -	u64 alloc = 0;
> > > +	u64 alloc = *(u64 *)data;
> > >
> > >  	if (levels == 5 && !pgtable_l5_enabled())
> > >  		levels = 4;
> > > @@ -1382,8 +1381,6 @@ static int __init __kpti_install_ng_mappings(void *__unused)
> > >
> > >  	if (!cpu) {
> > >  		int ret;
> > > -
> > > -		alloc = __get_free_pages(GFP_ATOMIC | __GFP_ZERO, order);
> > >  		kpti_ng_temp_pgd = (pgd_t *)(alloc + (levels - 1) * PAGE_SIZE);
> > >  		kpti_ng_temp_alloc = kpti_ng_temp_pgd_pa = __pa(kpti_ng_temp_pgd);
> > >
> > > @@ -1414,16 +1411,16 @@ static int __init __kpti_install_ng_mappings(void *__unused)
> > >  	remap_fn(cpu, num_online_cpus(), kpti_ng_temp_pgd_pa, KPTI_NG_TEMP_VA);
> > >  	cpu_uninstall_idmap();
> > >
> > > -	if (!cpu) {
> > > -		free_pages(alloc, order);
> > > +	if (!cpu)
> > >  		arm64_use_ng_mappings = true;
> > > -	}
> > >
> > >  	return 0;
> > >  }
> > >
> > >  void __init kpti_install_ng_mappings(void)
> > >  {
> > > +	int order = order_base_2(CONFIG_PGTABLE_LEVELS);
> > > +	u64 alloc;
> > >  	/* Check whether KPTI is going to be used */
> > >  	if (!arm64_kernel_unmapped_at_el0())
> > >  		return;
> > > @@ -1436,8 +1433,14 @@ void __init kpti_install_ng_mappings(void)
> > >  	if (arm64_use_ng_mappings)
> > >  		return;
> > >
> > > +	alloc = __get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
> > > +	if (!alloc)
> > > +		panic("Failed to alloc page tables\n");
> >
> > Why are you adding this panic?
> 
> Because original code call the panic() when it fails to create
> mapping of kpti_ng_temp_pgd and I think allocation is also part
> of creating kpti_ng_temp_pgd too.
> So, I added this panic() when allocation is failed for kpti_ng_temp_pgd.

No. The current code seems to assume the allocation will succeed and
panic()s if the call to __create_pgd_mapping_locked() returns an error.

Just make this:

	if (WARN_ON(!alloc))
		return;

Will

Re: [PATCH v5 3/3] arm64: mmu: avoid allocating pages while installing ng-mapping for KPTI

Posted by Yeoreum Yun 2 weeks, 6 days ago

> On Mon, Jan 19, 2026 at 09:30:30PM +0000, Yeoreum Yun wrote:
> > Hi Will,
> >
> > > On Mon, Jan 05, 2026 at 08:23:28PM +0000, Yeoreum Yun wrote:
> > > > The current __kpti_install_ng_mappings() allocates a temporary PGD
> > > > while installing the NG mapping for KPTI under stop_machine(),
> > > > using GFP_ATOMIC.
> > > >
> > > > This is fine in the non-PREEMPT_RT case. However, it becomes a problem
> > > > under PREEMPT_RT because generic memory allocation/free APIs
> > > > (e.g., pgtable_alloc(), __get_free_pages(), etc.) cannot be invoked
> > > > in a non-preemptible context, except for the *_nolock() variants.
> > > > These generic allocators may sleep due to their use of spin_lock().
> > > >
> > > > In other words, calling __get_free_pages(), even with GFP_ATOMIC,
> > > > is not allowed in __kpti_install_ng_mappings(), which is executed by
> > > > the stopper thread where preemption is disabled under PREEMPT_RT.
> > > >
> > > > To address this, preallocate the page needed for the temporary PGD
> > > > before invoking __kpti_install_ng_mappings() via stop_machine().
> > > >
> > > > Fixes: 47546a1912fc ("arm64: mm: install KPTI nG mappings with MMU enabled")
> > > > Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> > > > Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
> > > > ---
> > > >  arch/arm64/mm/mmu.c | 21 ++++++++++++---------
> > > >  1 file changed, 12 insertions(+), 9 deletions(-)
> > > >
> > > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> > > > index 120874a2d35b..6ea5b80ab54f 100644
> > > > --- a/arch/arm64/mm/mmu.c
> > > > +++ b/arch/arm64/mm/mmu.c
> > > > @@ -1360,7 +1360,7 @@ static phys_addr_t __init kpti_ng_pgd_alloc(enum pgtable_type type)
> > > >  	return kpti_ng_temp_alloc;
> > > >  }
> > > >
> > > > -static int __init __kpti_install_ng_mappings(void *__unused)
> > > > +static int __init __kpti_install_ng_mappings(void *data)
> > > >  {
> > > >  	typedef void (kpti_remap_fn)(int, int, phys_addr_t, unsigned long);
> > > >  	extern kpti_remap_fn idmap_kpti_install_ng_mappings;
> > > > @@ -1368,10 +1368,9 @@ static int __init __kpti_install_ng_mappings(void *__unused)
> > > >
> > > >  	int cpu = smp_processor_id();
> > > >  	int levels = CONFIG_PGTABLE_LEVELS;
> > > > -	int order = order_base_2(levels);
> > > >  	u64 kpti_ng_temp_pgd_pa = 0;
> > > >  	pgd_t *kpti_ng_temp_pgd;
> > > > -	u64 alloc = 0;
> > > > +	u64 alloc = *(u64 *)data;
> > > >
> > > >  	if (levels == 5 && !pgtable_l5_enabled())
> > > >  		levels = 4;
> > > > @@ -1382,8 +1381,6 @@ static int __init __kpti_install_ng_mappings(void *__unused)
> > > >
> > > >  	if (!cpu) {
> > > >  		int ret;
> > > > -
> > > > -		alloc = __get_free_pages(GFP_ATOMIC | __GFP_ZERO, order);
> > > >  		kpti_ng_temp_pgd = (pgd_t *)(alloc + (levels - 1) * PAGE_SIZE);
> > > >  		kpti_ng_temp_alloc = kpti_ng_temp_pgd_pa = __pa(kpti_ng_temp_pgd);
> > > >
> > > > @@ -1414,16 +1411,16 @@ static int __init __kpti_install_ng_mappings(void *__unused)
> > > >  	remap_fn(cpu, num_online_cpus(), kpti_ng_temp_pgd_pa, KPTI_NG_TEMP_VA);
> > > >  	cpu_uninstall_idmap();
> > > >
> > > > -	if (!cpu) {
> > > > -		free_pages(alloc, order);
> > > > +	if (!cpu)
> > > >  		arm64_use_ng_mappings = true;
> > > > -	}
> > > >
> > > >  	return 0;
> > > >  }
> > > >
> > > >  void __init kpti_install_ng_mappings(void)
> > > >  {
> > > > +	int order = order_base_2(CONFIG_PGTABLE_LEVELS);
> > > > +	u64 alloc;
> > > >  	/* Check whether KPTI is going to be used */
> > > >  	if (!arm64_kernel_unmapped_at_el0())
> > > >  		return;
> > > > @@ -1436,8 +1433,14 @@ void __init kpti_install_ng_mappings(void)
> > > >  	if (arm64_use_ng_mappings)
> > > >  		return;
> > > >
> > > > +	alloc = __get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
> > > > +	if (!alloc)
> > > > +		panic("Failed to alloc page tables\n");
> > >
> > > Why are you adding this panic?
> >
> > Because original code call the panic() when it fails to create
> > mapping of kpti_ng_temp_pgd and I think allocation is also part
> > of creating kpti_ng_temp_pgd too.
> > So, I added this panic() when allocation is failed for kpti_ng_temp_pgd.
>
> No. The current code seems to assume the allocation will succeed and
> panic()s if the call to __create_pgd_mapping_locked() returns an error.
>
> Just make this:
>
> 	if (WARN_ON(!alloc))
> 		return;
>

Okay I'll change with this.

Thanks.

--
Sincerely,
Yeoreum Yun

[PATCH v5 1/3] arm64: mmu: introduce pgtable_alloc_t
[PATCH v5 2/3] arm64: mmu: avoid allocating pages while splitting the linear mapping
[PATCH v5 3/3] arm64: mmu: avoid allocating pages while installing ng-mapping for KPTI