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Message-ID: <38fb7875-88c0-4687-8421-f92ae3ffaa72@arm.com>
Date: Mon, 16 Jun 2025 11:04:26 +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 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>
> ---
> 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
> + 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).
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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