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Message-ID: <195ecf99-659c-4a1f-8418-e249c419dc38@arm.com>
Date: Mon, 23 Jun 2025 14:05:28 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Yang Shi <yang@...amperecomputing.com>, will@...nel.org,
catalin.marinas@....com, Miko.Lenczewski@....com, dev.jain@....com,
scott@...amperecomputing.com, cl@...two.org
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
Chaitanya S Prakash <chaitanyas.prakash@....com>
Subject: Re: [PATCH 2/4] arm64: mm: make __create_pgd_mapping() and helpers
non-void
On 17/06/2025 22:11, Yang Shi wrote:
>
>
> On 6/16/25 3:04 AM, Ryan Roberts wrote:
>> On 31/05/2025 03:41, Yang Shi wrote:
>>> The later patch will enhance __create_pgd_mapping() and related helpers
>>> to split kernel linear mapping, it requires have return value. So make
>>> __create_pgd_mapping() and helpers non-void functions.
>>>
>>> And move the BUG_ON() out of page table alloc helper since failing
>>> splitting kernel linear mapping is not fatal and can be handled by the
>>> callers in the later patch. Have BUG_ON() after
>>> __create_pgd_mapping_locked() returns to keep the current callers behavior
>>> intact.
>>>
>>> Suggested-by: Ryan Roberts <ryan.roberts@....com>
>>> Signed-off-by: Yang Shi <yang@...amperecomputing.com>
>> With the nits below taken care of:
>>
>> Reviewed-by: Ryan Roberts <ryan.roberts@....com>
>
> Thank you. Although this patch may be dropped in the new spin per our
> discussion, this is still needed to fix the memory hotplug bug.
Yep understood. Chaitanya (CCed) is looking into that so hopefully she can reuse
this patch.
Thanks,
Ryan
>
>>
>>> ---
>>> arch/arm64/kernel/cpufeature.c | 10 ++-
>>> arch/arm64/mm/mmu.c | 130 +++++++++++++++++++++++----------
>>> 2 files changed, 99 insertions(+), 41 deletions(-)
>>>
>>> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
>>> index 25e1fbfab6a3..e879bfcf853b 100644
>>> --- a/arch/arm64/kernel/cpufeature.c
>>> +++ b/arch/arm64/kernel/cpufeature.c
>>> @@ -1933,9 +1933,9 @@ static bool has_pmuv3(const struct
>>> arm64_cpu_capabilities *entry, int scope)
>>> #define KPTI_NG_TEMP_VA (-(1UL << PMD_SHIFT))
>>> extern
>>> -void create_kpti_ng_temp_pgd(pgd_t *pgdir, phys_addr_t phys, unsigned long
>>> virt,
>>> - phys_addr_t size, pgprot_t prot,
>>> - phys_addr_t (*pgtable_alloc)(int), int flags);
>>> +int create_kpti_ng_temp_pgd(pgd_t *pgdir, phys_addr_t phys, unsigned long virt,
>>> + phys_addr_t size, pgprot_t prot,
>>> + phys_addr_t (*pgtable_alloc)(int), int flags);
>>> static phys_addr_t __initdata kpti_ng_temp_alloc;
>>> @@ -1957,6 +1957,7 @@ static int __init __kpti_install_ng_mappings(void
>>> *__unused)
>>> u64 kpti_ng_temp_pgd_pa = 0;
>>> pgd_t *kpti_ng_temp_pgd;
>>> u64 alloc = 0;
>>> + int err;
>>> if (levels == 5 && !pgtable_l5_enabled())
>>> levels = 4;
>>> @@ -1986,9 +1987,10 @@ static int __init __kpti_install_ng_mappings(void
>>> *__unused)
>>> // covers the PTE[] page itself, the remaining entries are free
>>> // to be used as a ad-hoc fixmap.
>>> //
>>> - create_kpti_ng_temp_pgd(kpti_ng_temp_pgd, __pa(alloc),
>>> + err = create_kpti_ng_temp_pgd(kpti_ng_temp_pgd, __pa(alloc),
>>> KPTI_NG_TEMP_VA, PAGE_SIZE, PAGE_KERNEL,
>>> kpti_ng_pgd_alloc, 0);
>>> + BUG_ON(err);
>>> }
>>> cpu_install_idmap();
>>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>>> index ea6695d53fb9..775c0536b194 100644
>>> --- a/arch/arm64/mm/mmu.c
>>> +++ b/arch/arm64/mm/mmu.c
>>> @@ -189,15 +189,16 @@ static void init_pte(pte_t *ptep, unsigned long addr,
>>> unsigned long end,
>>> } while (ptep++, addr += PAGE_SIZE, addr != end);
>>> }
>>> -static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
>>> - unsigned long end, phys_addr_t phys,
>>> - pgprot_t prot,
>>> - phys_addr_t (*pgtable_alloc)(int),
>>> - int flags)
>>> +static int alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
>>> + unsigned long end, phys_addr_t phys,
>>> + pgprot_t prot,
>>> + phys_addr_t (*pgtable_alloc)(int),
>>> + int flags)
>>> {
>>> unsigned long next;
>>> pmd_t pmd = READ_ONCE(*pmdp);
>>> pte_t *ptep;
>>> + int ret = 0;
>>> BUG_ON(pmd_sect(pmd));
>>> if (pmd_none(pmd)) {
>>> @@ -208,6 +209,10 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned
>>> long addr,
>>> pmdval |= PMD_TABLE_PXN;
>>> BUG_ON(!pgtable_alloc);
>>> pte_phys = pgtable_alloc(PAGE_SHIFT);
>>> + if (pte_phys == -1) {
>> It would be better to have a macro definition for the invalid PA case instead of
>> using the magic -1 everywhere. I think it can be local to this file. Perhaps:
>>
>> #define INVAL_PHYS_ADDR -1
>
> OK
>
>>
>>> + ret = -ENOMEM;
>>> + goto out;
>>> + }
>>> ptep = pte_set_fixmap(pte_phys);
>>> init_clear_pgtable(ptep);
>>> ptep += pte_index(addr);
>>> @@ -239,13 +244,17 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned
>>> long addr,
>>> * walker.
>>> */
>>> pte_clear_fixmap();
>>> +
>>> +out:
>>> + return ret;
>>> }
>>> -static void init_pmd(pmd_t *pmdp, unsigned long addr, unsigned long end,
>>> - phys_addr_t phys, pgprot_t prot,
>>> - phys_addr_t (*pgtable_alloc)(int), int flags)
>>> +static int init_pmd(pmd_t *pmdp, unsigned long addr, unsigned long end,
>>> + phys_addr_t phys, pgprot_t prot,
>>> + phys_addr_t (*pgtable_alloc)(int), int flags)
>>> {
>>> unsigned long next;
>>> + int ret = 0;
>>> do {
>>> pmd_t old_pmd = READ_ONCE(*pmdp);
>>> @@ -264,22 +273,27 @@ static void init_pmd(pmd_t *pmdp, unsigned long addr,
>>> unsigned long end,
>>> BUG_ON(!pgattr_change_is_safe(pmd_val(old_pmd),
>>> READ_ONCE(pmd_val(*pmdp))));
>>> } else {
>>> - alloc_init_cont_pte(pmdp, addr, next, phys, prot,
>>> + ret = alloc_init_cont_pte(pmdp, addr, next, phys, prot,
>>> pgtable_alloc, flags);
>>> + if (ret)
>>> + break;
>>> BUG_ON(pmd_val(old_pmd) != 0 &&
>>> pmd_val(old_pmd) != READ_ONCE(pmd_val(*pmdp)));
>>> }
>>> phys += next - addr;
>>> } while (pmdp++, addr = next, addr != end);
>>> +
>>> + return ret;
>>> }
>>> -static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr,
>>> - unsigned long end, phys_addr_t phys,
>>> - pgprot_t prot,
>>> - phys_addr_t (*pgtable_alloc)(int), int flags)
>>> +static int alloc_init_cont_pmd(pud_t *pudp, unsigned long addr,
>>> + unsigned long end, phys_addr_t phys,
>>> + pgprot_t prot,
>>> + phys_addr_t (*pgtable_alloc)(int), int flags)
>>> {
>>> unsigned long next;
>>> + int ret = 0;
>>> pud_t pud = READ_ONCE(*pudp);
>>> pmd_t *pmdp;
>>> @@ -295,6 +309,10 @@ static void alloc_init_cont_pmd(pud_t *pudp, unsigned
>>> long addr,
>>> pudval |= PUD_TABLE_PXN;
>>> BUG_ON(!pgtable_alloc);
>>> pmd_phys = pgtable_alloc(PMD_SHIFT);
>>> + if (pmd_phys == -1) {
>>> + ret = -ENOMEM;
>>> + goto out;
>>> + }
>>> pmdp = pmd_set_fixmap(pmd_phys);
>>> init_clear_pgtable(pmdp);
>>> pmdp += pmd_index(addr);
>>> @@ -314,21 +332,27 @@ static void alloc_init_cont_pmd(pud_t *pudp, unsigned
>>> long addr,
>>> (flags & NO_CONT_MAPPINGS) == 0)
>>> __prot = __pgprot(pgprot_val(prot) | PTE_CONT);
>>> - init_pmd(pmdp, addr, next, phys, __prot, pgtable_alloc, flags);
>>> + ret = init_pmd(pmdp, addr, next, phys, __prot, pgtable_alloc, flags);
>>> + if (ret)
>>> + break;
>>> pmdp += pmd_index(next) - pmd_index(addr);
>>> phys += next - addr;
>>> } while (addr = next, addr != end);
>>> pmd_clear_fixmap();
>>> +
>>> +out:
>>> + return ret;
>>> }
>>> -static void alloc_init_pud(p4d_t *p4dp, unsigned long addr, unsigned long
>>> end,
>>> - phys_addr_t phys, pgprot_t prot,
>>> - phys_addr_t (*pgtable_alloc)(int),
>>> - int flags)
>>> +static int alloc_init_pud(p4d_t *p4dp, unsigned long addr, unsigned long end,
>>> + phys_addr_t phys, pgprot_t prot,
>>> + phys_addr_t (*pgtable_alloc)(int),
>>> + int flags)
>>> {
>>> unsigned long next;
>>> + int ret = 0;
>>> p4d_t p4d = READ_ONCE(*p4dp);
>>> pud_t *pudp;
>>> @@ -340,6 +364,10 @@ static void alloc_init_pud(p4d_t *p4dp, unsigned long
>>> addr, unsigned long end,
>>> p4dval |= P4D_TABLE_PXN;
>>> BUG_ON(!pgtable_alloc);
>>> pud_phys = pgtable_alloc(PUD_SHIFT);
>>> + if (pud_phys == -1) {
>>> + ret = -ENOMEM;
>>> + goto out;
>>> + }
>>> pudp = pud_set_fixmap(pud_phys);
>>> init_clear_pgtable(pudp);
>>> pudp += pud_index(addr);
>>> @@ -369,8 +397,10 @@ static void alloc_init_pud(p4d_t *p4dp, unsigned long
>>> addr, unsigned long end,
>>> BUG_ON(!pgattr_change_is_safe(pud_val(old_pud),
>>> READ_ONCE(pud_val(*pudp))));
>>> } else {
>>> - alloc_init_cont_pmd(pudp, addr, next, phys, prot,
>>> + ret = alloc_init_cont_pmd(pudp, addr, next, phys, prot,
>>> pgtable_alloc, flags);
>>> + if (ret)
>>> + break;
>>> BUG_ON(pud_val(old_pud) != 0 &&
>>> pud_val(old_pud) != READ_ONCE(pud_val(*pudp)));
>>> @@ -379,14 +409,18 @@ static void alloc_init_pud(p4d_t *p4dp, unsigned long
>>> addr, unsigned long end,
>>> } while (pudp++, addr = next, addr != end);
>>> pud_clear_fixmap();
>>> +
>>> +out:
>>> + return ret;
>>> }
>>> -static void alloc_init_p4d(pgd_t *pgdp, unsigned long addr, unsigned long
>>> end,
>>> - phys_addr_t phys, pgprot_t prot,
>>> - phys_addr_t (*pgtable_alloc)(int),
>>> - int flags)
>>> +static int alloc_init_p4d(pgd_t *pgdp, unsigned long addr, unsigned long end,
>>> + phys_addr_t phys, pgprot_t prot,
>>> + phys_addr_t (*pgtable_alloc)(int),
>>> + int flags)
>>> {
>>> unsigned long next;
>>> + int ret = 0;
>>> pgd_t pgd = READ_ONCE(*pgdp);
>>> p4d_t *p4dp;
>>> @@ -398,6 +432,10 @@ static void alloc_init_p4d(pgd_t *pgdp, unsigned long
>>> addr, unsigned long end,
>>> pgdval |= PGD_TABLE_PXN;
>>> BUG_ON(!pgtable_alloc);
>>> p4d_phys = pgtable_alloc(P4D_SHIFT);
>>> + if (p4d_phys == -1) {
>>> + ret = -ENOMEM;
>>> + goto out;
>>> + }
>>> p4dp = p4d_set_fixmap(p4d_phys);
>>> init_clear_pgtable(p4dp);
>>> p4dp += p4d_index(addr);
>>> @@ -412,8 +450,10 @@ static void alloc_init_p4d(pgd_t *pgdp, unsigned long
>>> addr, unsigned long end,
>>> next = p4d_addr_end(addr, end);
>>> - alloc_init_pud(p4dp, addr, next, phys, prot,
>>> + ret = alloc_init_pud(p4dp, addr, next, phys, prot,
>>> pgtable_alloc, flags);
>>> + if (ret)
>>> + break;
>>> BUG_ON(p4d_val(old_p4d) != 0 &&
>>> p4d_val(old_p4d) != READ_ONCE(p4d_val(*p4dp)));
>>> @@ -422,23 +462,27 @@ static void alloc_init_p4d(pgd_t *pgdp, unsigned long
>>> addr, unsigned long end,
>>> } while (p4dp++, addr = next, addr != end);
>>> p4d_clear_fixmap();
>>> +
>>> +out:
>>> + return ret;
>>> }
>>> -static void __create_pgd_mapping_locked(pgd_t *pgdir, phys_addr_t phys,
>>> - unsigned long virt, phys_addr_t size,
>>> - pgprot_t prot,
>>> - phys_addr_t (*pgtable_alloc)(int),
>>> - int flags)
>>> +static int __create_pgd_mapping_locked(pgd_t *pgdir, phys_addr_t phys,
>>> + unsigned long virt, phys_addr_t size,
>>> + pgprot_t prot,
>>> + phys_addr_t (*pgtable_alloc)(int),
>>> + int flags)
>>> {
>>> unsigned long addr, end, next;
>>> pgd_t *pgdp = pgd_offset_pgd(pgdir, virt);
>>> + int ret = 0;
>>> /*
>>> * If the virtual and physical address don't have the same offset
>>> * within a page, we cannot map the region as the caller expects.
>>> */
>>> if (WARN_ON((phys ^ virt) & ~PAGE_MASK))
>>> - return;
>>> + return -EINVAL;
>>> phys &= PAGE_MASK;
>>> addr = virt & PAGE_MASK;
>>> @@ -446,10 +490,14 @@ static void __create_pgd_mapping_locked(pgd_t *pgdir,
>>> phys_addr_t phys,
>>> do {
>>> next = pgd_addr_end(addr, end);
>>> - alloc_init_p4d(pgdp, addr, next, phys, prot, pgtable_alloc,
>>> + ret = alloc_init_p4d(pgdp, addr, next, phys, prot, pgtable_alloc,
>>> flags);
>>> + if (ret)
>>> + break;
>>> phys += next - addr;
>>> } while (pgdp++, addr = next, addr != end);
>>> +
>>> + return ret;
>>> }
>>> static void __create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys,
>>> @@ -458,17 +506,20 @@ static void __create_pgd_mapping(pgd_t *pgdir,
>>> phys_addr_t phys,
>>> phys_addr_t (*pgtable_alloc)(int),
>>> int flags)
>>> {
>>> + int err;
>>> +
>>> mutex_lock(&fixmap_lock);
>>> - __create_pgd_mapping_locked(pgdir, phys, virt, size, prot,
>>> - pgtable_alloc, flags);
>>> + err = __create_pgd_mapping_locked(pgdir, phys, virt, size, prot,
>>> + pgtable_alloc, flags);
>>> + BUG_ON(err);
>>> mutex_unlock(&fixmap_lock);
>>> }
>>> #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
>>> extern __alias(__create_pgd_mapping_locked)
>>> -void create_kpti_ng_temp_pgd(pgd_t *pgdir, phys_addr_t phys, unsigned long
>>> virt,
>>> - phys_addr_t size, pgprot_t prot,
>>> - phys_addr_t (*pgtable_alloc)(int), int flags);
>>> +int create_kpti_ng_temp_pgd(pgd_t *pgdir, phys_addr_t phys, unsigned long virt,
>>> + phys_addr_t size, pgprot_t prot,
>>> + phys_addr_t (*pgtable_alloc)(int), int flags);
>>> #endif
>> Personally I would have converted this from an alias to a wrapper:
>>
>> void create_kpti_ng_temp_pgd(pgd_t *pgdir, phys_addr_t phys, unsigned long virt,
>> phys_addr_t size, pgprot_t prot,
>> phys_addr_t (*pgtable_alloc)(int), int flags)
>> {
>> int ret;
>>
>> ret = __create_pgd_mapping_locked(pgdir, phys, virt, size, prot,
>> pgtable_alloc, flags);
>> BUG_ON(err);
>> }
>>
>> Then there is no churn in cpufeature.c. But it's not a strong opinion. If you
>> prefer it like this then I'm ok with it (We'll need to see what Catalin and Will
>> prefer ultimately anyway).
>
> I don't have strong preference either.
>
> Thanks,
> Yang
>
>>
>> Thanks,
>> Ryan
>>
>>> static phys_addr_t __pgd_pgtable_alloc(int shift)
>>> @@ -476,13 +527,17 @@ static phys_addr_t __pgd_pgtable_alloc(int shift)
>>> /* Page is zeroed by init_clear_pgtable() so don't duplicate effort. */
>>> void *ptr = (void *)__get_free_page(GFP_PGTABLE_KERNEL & ~__GFP_ZERO);
>>> - BUG_ON(!ptr);
>>> + if (!ptr)
>>> + return -1;
>>> +
>>> return __pa(ptr);
>>> }
>>> static phys_addr_t pgd_pgtable_alloc(int shift)
>>> {
>>> phys_addr_t pa = __pgd_pgtable_alloc(shift);
>>> + if (pa == -1)
>>> + goto out;
>>> struct ptdesc *ptdesc = page_ptdesc(phys_to_page(pa));
>>> /*
>>> @@ -498,6 +553,7 @@ static phys_addr_t pgd_pgtable_alloc(int shift)
>>> else if (shift == PMD_SHIFT)
>>> BUG_ON(!pagetable_pmd_ctor(ptdesc));
>>> +out:
>>> return pa;
>>> }
>>>
>
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