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Message-ID: <96cea729-437a-4bd8-8dbf-7ff651979387@os.amperecomputing.com>
Date: Tue, 17 Jun 2025 14:11:20 -0700
From: Yang Shi <yang@...amperecomputing.com>
To: Ryan Roberts <ryan.roberts@....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 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.
>
>> ---
>> 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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