[PATCH 0/2] arm64: errata: Workaround Cortex-A715 errata #2645198

[PATCH 0/2] arm64: errata: Workaround Cortex-A715 errata #2645198

[Anshuman Khandual]

This series adds Cortex-A715 partnumber and workarounds the errata #2645198
which gets triggered when an userspace page mapping permission changes from
executable to non-executable, corrupting both ESR_EL1/FAR_EL1 registers
when an instruction abort is taken.

This series applies on v6.1-rc1.

The errata description can be found here.

https://developer.arm.com/documentation/SDEN2148827/1000/?lang=en

Cc: Catalin Marinas <catalin.marinas@arm.com> 
Cc: Will Deacon <will@kernel.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Mark Rutland <mark.rutland@arm.com> 
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-doc@vger.kernel.org

Anshuman Khandual (2):
  arm64: Add Cortex-715 CPU part definition
  arm64: errata: Workaround possible Cortex-A715 [ESR|FAR]_ELx corruption

 Documentation/arm64/silicon-errata.rst |  2 ++
 arch/arm64/Kconfig                     | 16 +++++++++++
 arch/arm64/include/asm/cputype.h       |  2 ++
 arch/arm64/include/asm/hugetlb.h       |  9 +++++++
 arch/arm64/include/asm/pgtable.h       | 24 +++++++++++++++++
 arch/arm64/kernel/cpu_errata.c         |  7 +++++
 arch/arm64/mm/hugetlbpage.c            | 37 ++++++++++++++++++++++++++
 arch/arm64/tools/cpucaps               |  1 +
 8 files changed, 98 insertions(+)

-- 
2.25.1

[PATCH 1/2] arm64: Add Cortex-715 CPU part definition

[Anshuman Khandual]

Add the CPU Partnumbers for the new Arm designs.

Cc: Catalin Marinas <catalin.marinas@arm.com> 
Cc: Will Deacon <will@kernel.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
 arch/arm64/include/asm/cputype.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm64/include/asm/cputype.h b/arch/arm64/include/asm/cputype.h
index abc418650fec..4b1ad810436f 100644
--- a/arch/arm64/include/asm/cputype.h
+++ b/arch/arm64/include/asm/cputype.h
@@ -80,6 +80,7 @@
 #define ARM_CPU_PART_CORTEX_X1		0xD44
 #define ARM_CPU_PART_CORTEX_A510	0xD46
 #define ARM_CPU_PART_CORTEX_A710	0xD47
+#define ARM_CPU_PART_CORTEX_A715	0xD4D
 #define ARM_CPU_PART_CORTEX_X2		0xD48
 #define ARM_CPU_PART_NEOVERSE_N2	0xD49
 #define ARM_CPU_PART_CORTEX_A78C	0xD4B
@@ -142,6 +143,7 @@
 #define MIDR_CORTEX_X1	MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_X1)
 #define MIDR_CORTEX_A510 MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A510)
 #define MIDR_CORTEX_A710 MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A710)
+#define MIDR_CORTEX_A715 MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A715)
 #define MIDR_CORTEX_X2 MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_X2)
 #define MIDR_NEOVERSE_N2 MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_NEOVERSE_N2)
 #define MIDR_CORTEX_A78C	MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A78C)
-- 
2.25.1

[PATCH 2/2] arm64: errata: Workaround possible Cortex-A715 [ESR|FAR]_ELx corruption

[Anshuman Khandual]

If a Cortex-A715 cpu sees a page mapping permissions change from executable
to non-executable, it may corrupt the ESR_ELx and FAR_ELx registers, on the
next instruction abort caused by permission fault.

Only user-space does executable to non-executable permission transition via
mprotect() system call which calls ptep_modify_prot_start() and ptep_modify
_prot_commit() helpers, while changing the page mapping. The platform code
can override these helpers via __HAVE_ARCH_PTEP_MODIFY_PROT_TRANSACTION.

Work around the problem via doing a break-before-make TLB invalidation, for
all executable user space mappings, that go through mprotect() system call.
This overrides ptep_modify_prot_start() and ptep_modify_prot_commit(), via
defining HAVE_ARCH_PTEP_MODIFY_PROT_TRANSACTION on the platform thus giving
an opportunity to intercept user space exec mappings, and do the necessary
TLB invalidation. Similar interceptions are also implemented for HugeTLB.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Mark Rutland <mark.rutland@arm.com> 
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
 Documentation/arm64/silicon-errata.rst |  2 ++
 arch/arm64/Kconfig                     | 16 +++++++++++
 arch/arm64/include/asm/hugetlb.h       |  9 +++++++
 arch/arm64/include/asm/pgtable.h       | 24 +++++++++++++++++
 arch/arm64/kernel/cpu_errata.c         |  7 +++++
 arch/arm64/mm/hugetlbpage.c            | 37 ++++++++++++++++++++++++++
 arch/arm64/tools/cpucaps               |  1 +
 7 files changed, 96 insertions(+)

diff --git a/Documentation/arm64/silicon-errata.rst b/Documentation/arm64/silicon-errata.rst
index 808ade4cc008..ec5f889d7681 100644
--- a/Documentation/arm64/silicon-errata.rst
+++ b/Documentation/arm64/silicon-errata.rst
@@ -120,6 +120,8 @@ stable kernels.
 +----------------+-----------------+-----------------+-----------------------------+
 | ARM            | Cortex-A710     | #2224489        | ARM64_ERRATUM_2224489       |
 +----------------+-----------------+-----------------+-----------------------------+
+| ARM            | Cortex-A715     | #2645198        | ARM64_ERRATUM_2645198       |
++----------------+-----------------+-----------------+-----------------------------+
 | ARM            | Cortex-X2       | #2119858        | ARM64_ERRATUM_2119858       |
 +----------------+-----------------+-----------------+-----------------------------+
 | ARM            | Cortex-X2       | #2224489        | ARM64_ERRATUM_2224489       |
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 505c8a1ccbe0..56c3381e9d94 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -964,6 +964,22 @@ config ARM64_ERRATUM_2457168
 
 	  If unsure, say Y.
 
+config ARM64_ERRATUM_2645198
+	bool "Cortex-A715: 2645198: Workaround possible [ESR|FAR]_ELx corruption"
+	default y
+	help
+	  This option adds the workaround for ARM Cortex-A715 erratum 2645198.
+
+	  If a Cortex-A715 cpu sees a page mapping permissions change from executable
+	  to non-executable, it may corrupt the ESR_ELx and FAR_ELx registers on the
+	  next instruction abort caused by permission fault.
+
+	  Only user-space does executable to non-executable permission transition via
+	  mprotect() system call. Workaround the problem by doing a break-before-make
+	  TLB invalidation, for all changes to executable user space mappings.
+
+	  If unsure, say Y.
+
 config CAVIUM_ERRATUM_22375
 	bool "Cavium erratum 22375, 24313"
 	default y
diff --git a/arch/arm64/include/asm/hugetlb.h b/arch/arm64/include/asm/hugetlb.h
index d20f5da2d76f..6a4a1ab8eb23 100644
--- a/arch/arm64/include/asm/hugetlb.h
+++ b/arch/arm64/include/asm/hugetlb.h
@@ -49,6 +49,15 @@ extern pte_t huge_ptep_get(pte_t *ptep);
 
 void __init arm64_hugetlb_cma_reserve(void);
 
+#define huge_ptep_modify_prot_start huge_ptep_modify_prot_start
+extern pte_t huge_ptep_modify_prot_start(struct vm_area_struct *vma,
+					 unsigned long addr, pte_t *ptep);
+
+#define huge_ptep_modify_prot_commit huge_ptep_modify_prot_commit
+extern void huge_ptep_modify_prot_commit(struct vm_area_struct *vma,
+					 unsigned long addr, pte_t *ptep,
+					 pte_t old_pte, pte_t new_pte);
+
 #include <asm-generic/hugetlb.h>
 
 #endif /* __ASM_HUGETLB_H */
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 71a1af42f0e8..c4c021277f20 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -1095,7 +1095,31 @@ static inline bool pud_sect_supported(void)
 	return PAGE_SIZE == SZ_4K;
 }
 
+#define __HAVE_ARCH_PTEP_MODIFY_PROT_TRANSACTION
+static inline pte_t ptep_modify_prot_start(struct vm_area_struct *vma,
+					   unsigned long addr,
+					   pte_t *ptep)
+{
+	pte_t pte = ptep_get_and_clear(vma->vm_mm, addr, ptep);
 
+	if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198)) {
+		/*
+		 * Break-before-make (BBM) is required for all user space mappings
+		 * when the permission changes from executable to non-executable
+		 * in cases where cpu is affected with errata #2645198.
+		 */
+		if (pte_user_exec(pte) && cpus_have_const_cap(ARM64_WORKAROUND_2645198))
+			__flush_tlb_range(vma, addr, addr + PAGE_SIZE, PAGE_SIZE, false, 3);
+	}
+	return pte;
+}
+
+static inline void ptep_modify_prot_commit(struct vm_area_struct *vma,
+					   unsigned long addr,
+					   pte_t *ptep, pte_t old_pte, pte_t pte)
+{
+	__set_pte_at(vma->vm_mm, addr, ptep, pte);
+}
 #endif /* !__ASSEMBLY__ */
 
 #endif /* __ASM_PGTABLE_H */
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 89ac00084f38..307faa2b4395 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -661,6 +661,13 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
 		CAP_MIDR_RANGE_LIST(trbe_write_out_of_range_cpus),
 	},
 #endif
+#ifdef CONFIG_ARM64_ERRATUM_2645198
+	{
+		.desc = "ARM erratum 2645198",
+		.capability = ARM64_WORKAROUND_2645198,
+		ERRATA_MIDR_ALL_VERSIONS(MIDR_CORTEX_A715)
+	},
+#endif
 #ifdef CONFIG_ARM64_ERRATUM_2077057
 	{
 		.desc = "ARM erratum 2077057",
diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index 35e9a468d13e..8cdcb3a34c27 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -559,3 +559,40 @@ bool __init arch_hugetlb_valid_size(unsigned long size)
 {
 	return __hugetlb_valid_size(size);
 }
+
+pte_t huge_ptep_modify_prot_start(struct vm_area_struct *vma,
+				  unsigned long addr, pte_t *ptep)
+{
+	pte_t pte = huge_ptep_get_and_clear(vma->vm_mm, addr, ptep);
+
+	if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198)) {
+		/*
+		 * Break-before-make (BBM) is required for all user space mappings
+		 * when the permission changes from executable to non-executable
+		 * in cases where cpu is affected with errata #2645198.
+		 */
+		if (pte_user_exec(pte) && cpus_have_const_cap(ARM64_WORKAROUND_2645198)) {
+			size_t pgsize = page_size(pte_page(pte));
+			int level = 3;
+
+			if (pgsize == PUD_SIZE)
+				level = 1;
+			else if ((pgsize == PMD_SIZE) || (pgsize == CONT_PMD_SIZE))
+				level = 2;
+			else if (pgsize == CONT_PTE_SIZE)
+				level = 3;
+			else
+				pr_warn("%s: unrecognized huge page size 0x%lx\n",
+					__func__, pgsize);
+			__flush_tlb_range(vma, addr, addr + pgsize, pgsize, false, level);
+		}
+	}
+	return pte;
+}
+
+void huge_ptep_modify_prot_commit(struct vm_area_struct *vma,
+				  unsigned long addr, pte_t *ptep,
+				  pte_t old_pte, pte_t pte)
+{
+	set_huge_pte_at(vma->vm_mm, addr, ptep, pte);
+}
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index f1c0347ec31a..2274d836fcfe 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -70,6 +70,7 @@ WORKAROUND_2038923
 WORKAROUND_2064142
 WORKAROUND_2077057
 WORKAROUND_2457168
+WORKAROUND_2645198
 WORKAROUND_2658417
 WORKAROUND_TRBE_OVERWRITE_FILL_MODE
 WORKAROUND_TSB_FLUSH_FAILURE
-- 
2.25.1

Re: [PATCH 2/2] arm64: errata: Workaround possible Cortex-A715 [ESR|FAR]_ELx corruption

[Catalin Marinas]

On Thu, Oct 27, 2022 at 08:09:15AM +0530, Anshuman Khandual wrote:
> +#define __HAVE_ARCH_PTEP_MODIFY_PROT_TRANSACTION
> +static inline pte_t ptep_modify_prot_start(struct vm_area_struct *vma,
> +					   unsigned long addr,
> +					   pte_t *ptep)
> +{
> +	pte_t pte = ptep_get_and_clear(vma->vm_mm, addr, ptep);
>  
> +	if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198)) {
> +		/*
> +		 * Break-before-make (BBM) is required for all user space mappings
> +		 * when the permission changes from executable to non-executable
> +		 * in cases where cpu is affected with errata #2645198.
> +		 */
> +		if (pte_user_exec(pte) && cpus_have_const_cap(ARM64_WORKAROUND_2645198))
> +			__flush_tlb_range(vma, addr, addr + PAGE_SIZE, PAGE_SIZE, false, 3);

Why not flush_tlb_page() here?

But more importantly, can we not use ptep_clear_flush() instead (and
huge_ptep_clear_flush())? They return the pte and do the TLBI.

-- 
Catalin

Re: [PATCH 2/2] arm64: errata: Workaround possible Cortex-A715 [ESR|FAR]_ELx corruption

[Anshuman Khandual]

On 11/10/22 00:48, Catalin Marinas wrote:
> On Thu, Oct 27, 2022 at 08:09:15AM +0530, Anshuman Khandual wrote:
>> +#define __HAVE_ARCH_PTEP_MODIFY_PROT_TRANSACTION
>> +static inline pte_t ptep_modify_prot_start(struct vm_area_struct *vma,
>> +					   unsigned long addr,
>> +					   pte_t *ptep)
>> +{
>> +	pte_t pte = ptep_get_and_clear(vma->vm_mm, addr, ptep);
>>  
>> +	if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198)) {
>> +		/*
>> +		 * Break-before-make (BBM) is required for all user space mappings
>> +		 * when the permission changes from executable to non-executable
>> +		 * in cases where cpu is affected with errata #2645198.
>> +		 */
>> +		if (pte_user_exec(pte) && cpus_have_const_cap(ARM64_WORKAROUND_2645198))
>> +			__flush_tlb_range(vma, addr, addr + PAGE_SIZE, PAGE_SIZE, false, 3);
> 
> Why not flush_tlb_page() here?
> 
> But more importantly, can we not use ptep_clear_flush() instead (and

Something like ...

ptep_modify_prot_start -

if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198)) {
	if (pte_user_exec(READ_ONCE(*ptep)) && cpus_have_const_cap(ARM64_WORKAROUND_2645198))
		return ptep_clear_flush(vma, addr, ptep);
} else {
	return ptep_get_and_clear(vma->vm_mm, addr, ptep);
}

> huge_ptep_clear_flush())? They return the pte and do the TLBI.

huge_ptep_modify_prot_start -

if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198)) {
	if (pte_user_exec(READ_ONCE(*ptep)) && cpus_have_const_cap(ARM64_WORKAROUND_2645198))
		return huge_ptep_clear_flush(vma, addr, ptep);
} else {
	return huge_ptep_get_and_clear(vma->vm_mm, addr, ptep);
}

pte_user_exec(READ_ONCE(*ptep) should identify an user exec mapping even though
ptep represents a cont PTE/PMD huge page ? OR should huge_ptep_get() helper be
used instead ? Regardless, using [huge_]ptep_clear_flush() here seems better.

Re: [PATCH 2/2] arm64: errata: Workaround possible Cortex-A715 [ESR|FAR]_ELx corruption

[Catalin Marinas]

On Thu, Nov 10, 2022 at 08:45:07AM +0530, Anshuman Khandual wrote:
> On 11/10/22 00:48, Catalin Marinas wrote:
> > On Thu, Oct 27, 2022 at 08:09:15AM +0530, Anshuman Khandual wrote:
> >> +#define __HAVE_ARCH_PTEP_MODIFY_PROT_TRANSACTION
> >> +static inline pte_t ptep_modify_prot_start(struct vm_area_struct *vma,
> >> +					   unsigned long addr,
> >> +					   pte_t *ptep)
> >> +{
> >> +	pte_t pte = ptep_get_and_clear(vma->vm_mm, addr, ptep);
> >>  
> >> +	if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198)) {
> >> +		/*
> >> +		 * Break-before-make (BBM) is required for all user space mappings
> >> +		 * when the permission changes from executable to non-executable
> >> +		 * in cases where cpu is affected with errata #2645198.
> >> +		 */
> >> +		if (pte_user_exec(pte) && cpus_have_const_cap(ARM64_WORKAROUND_2645198))
> >> +			__flush_tlb_range(vma, addr, addr + PAGE_SIZE, PAGE_SIZE, false, 3);
> > 
> > Why not flush_tlb_page() here?
> > 
> > But more importantly, can we not use ptep_clear_flush() instead (and
> 
> Something like ...
> 
> ptep_modify_prot_start -
> 
> if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198)) {
> 	if (pte_user_exec(READ_ONCE(*ptep)) && cpus_have_const_cap(ARM64_WORKAROUND_2645198))
> 		return ptep_clear_flush(vma, addr, ptep);
> } else {
> 	return ptep_get_and_clear(vma->vm_mm, addr, ptep);
> }

Yes, this should work but avoid the 'else' when you have a return, so
something like:

	if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198) &&
	    cpus_have_const_cap(ARM64_WORKAROUND_2645198) &&
	    pte_user_exec(READ_ONCE(*ptep)))
		return ptep_clear_flush(vma, addr, ptep);

	return ptep_get_and_clear(vma->vm_mm, addr, ptep);


> > huge_ptep_clear_flush())? They return the pte and do the TLBI.
> 
> huge_ptep_modify_prot_start -
> 
> if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198)) {
> 	if (pte_user_exec(READ_ONCE(*ptep)) && cpus_have_const_cap(ARM64_WORKAROUND_2645198))
> 		return huge_ptep_clear_flush(vma, addr, ptep);
> } else {
> 	return huge_ptep_get_and_clear(vma->vm_mm, addr, ptep);
> }
> 
> pte_user_exec(READ_ONCE(*ptep) should identify an user exec mapping even though
> ptep represents a cont PTE/PMD huge page ? OR should huge_ptep_get() helper be
> used instead ?

This should work as a shortcut. The contiguous ptes should all be the
same, so it's sufficient to check one of them.

-- 
Catalin

Re: [PATCH 2/2] arm64: errata: Workaround possible Cortex-A715 [ESR|FAR]_ELx corruption

[Anshuman Khandual]

On 11/12/22 04:06, Catalin Marinas wrote:
> On Thu, Nov 10, 2022 at 08:45:07AM +0530, Anshuman Khandual wrote:
>> On 11/10/22 00:48, Catalin Marinas wrote:
>>> On Thu, Oct 27, 2022 at 08:09:15AM +0530, Anshuman Khandual wrote:
>>>> +#define __HAVE_ARCH_PTEP_MODIFY_PROT_TRANSACTION
>>>> +static inline pte_t ptep_modify_prot_start(struct vm_area_struct *vma,
>>>> +					   unsigned long addr,
>>>> +					   pte_t *ptep)
>>>> +{
>>>> +	pte_t pte = ptep_get_and_clear(vma->vm_mm, addr, ptep);
>>>>  
>>>> +	if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198)) {
>>>> +		/*
>>>> +		 * Break-before-make (BBM) is required for all user space mappings
>>>> +		 * when the permission changes from executable to non-executable
>>>> +		 * in cases where cpu is affected with errata #2645198.
>>>> +		 */
>>>> +		if (pte_user_exec(pte) && cpus_have_const_cap(ARM64_WORKAROUND_2645198))
>>>> +			__flush_tlb_range(vma, addr, addr + PAGE_SIZE, PAGE_SIZE, false, 3);
>>>
>>> Why not flush_tlb_page() here?
>>>
>>> But more importantly, can we not use ptep_clear_flush() instead (and
>>
>> Something like ...
>>
>> ptep_modify_prot_start -
>>
>> if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198)) {
>> 	if (pte_user_exec(READ_ONCE(*ptep)) && cpus_have_const_cap(ARM64_WORKAROUND_2645198))
>> 		return ptep_clear_flush(vma, addr, ptep);
>> } else {
>> 	return ptep_get_and_clear(vma->vm_mm, addr, ptep);
>> }
> 
> Yes, this should work but avoid the 'else' when you have a return, so
> something like:
> 
> 	if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198) &&
> 	    cpus_have_const_cap(ARM64_WORKAROUND_2645198) &&
> 	    pte_user_exec(READ_ONCE(*ptep)))
> 		return ptep_clear_flush(vma, addr, ptep);
> 
> 	return ptep_get_and_clear(vma->vm_mm, addr, ptep);

Right, realized that later.

> 
> 
>>> huge_ptep_clear_flush())? They return the pte and do the TLBI.
>>
>> huge_ptep_modify_prot_start -
>>
>> if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198)) {
>> 	if (pte_user_exec(READ_ONCE(*ptep)) && cpus_have_const_cap(ARM64_WORKAROUND_2645198))
>> 		return huge_ptep_clear_flush(vma, addr, ptep);
>> } else {
>> 	return huge_ptep_get_and_clear(vma->vm_mm, addr, ptep);
>> }
>>
>> pte_user_exec(READ_ONCE(*ptep) should identify an user exec mapping even though
>> ptep represents a cont PTE/PMD huge page ? OR should huge_ptep_get() helper be
>> used instead ?
> 
> This should work as a shortcut. The contiguous ptes should all be the
> same, so it's sufficient to check one of them.

Sure, will read the first one.