linux-kernel - Re: [PATCH v2 1/3] vmalloc: Choose a better start address in vm_area_register

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Message-ID: <d2280ab3-2c31-7525-b03d-b4717273b2c3@huawei.com>
Date:   Thu, 5 Aug 2021 20:46:20 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Catalin Marinas <catalin.marinas@....com>
CC:     Will Deacon <will@...nel.org>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <kasan-dev@...glegroups.com>,
        <linux-mm@...ck.org>
Subject: Re: [PATCH v2 1/3] vmalloc: Choose a better start address in
 vm_area_register_early()


On 2021/8/4 19:14, Catalin Marinas wrote:
> On Mon, Aug 02, 2021 at 10:39:04AM +0800, Kefeng Wang wrote:
>> On 2021/8/1 23:23, Catalin Marinas wrote:
>>> On Tue, Jul 20, 2021 at 10:51:03AM +0800, Kefeng Wang wrote:
>>>> There are some fixed locations in the vmalloc area be reserved
>>>> in ARM(see iotable_init()) and ARM64(see map_kernel()), but for
>>>> pcpu_page_first_chunk(), it calls vm_area_register_early() and
>>>> choose VMALLOC_START as the start address of vmap area which
>>>> could be conflicted with above address, then could trigger a
>>>> BUG_ON in vm_area_add_early().
>>>>
>>>> Let's choose the end of existing address range in vmlist as the
>>>> start address instead of VMALLOC_START to avoid the BUG_ON.
>>>>
>>>> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
>>>> ---
>>>>    mm/vmalloc.c | 8 +++++---
>>>>    1 file changed, 5 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
>>>> index d5cd52805149..a98cf97f032f 100644
>>>> --- a/mm/vmalloc.c
>>>> +++ b/mm/vmalloc.c
>>>> @@ -2238,12 +2238,14 @@ void __init vm_area_add_early(struct vm_struct *vm)
>>>>     */
>>>>    void __init vm_area_register_early(struct vm_struct *vm, size_t align)
>>>>    {
>>>> -	static size_t vm_init_off __initdata;
>>>> +	unsigned long vm_start = VMALLOC_START;
>>>> +	struct vm_struct *tmp;
>>>>    	unsigned long addr;
>>>> -	addr = ALIGN(VMALLOC_START + vm_init_off, align);
>>>> -	vm_init_off = PFN_ALIGN(addr + vm->size) - VMALLOC_START;
>>>> +	for (tmp = vmlist; tmp; tmp = tmp->next)
>>>> +		vm_start = (unsigned long)tmp->addr + tmp->size;
>>>> +	addr = ALIGN(vm_start, align);
>>>>    	vm->addr = (void *)addr;
>>>>    	vm_area_add_early(vm);
>>> Is there a risk of breaking other architectures? It doesn't look like to
>>> me but I thought I'd ask.
>> Before this patch, vm_init_off is to record the offset from VMALLOC_START,
>>
>> but it use VMALLOC_START as start address on the function
>> vm_area_register_early()
>>
>> called firstly,  this will cause the BUG_ON.
>>
>> With this patch, the most important change is that we choose the start
>> address via
>>
>> dynamic calculate the 'start' address by traversing the list.
>>
>> [wkf@...alhost linux-next]$ git grep vm_area_register_early
>> arch/alpha/mm/init.c: vm_area_register_early(&console_remap_vm, PAGE_SIZE);
>> arch/x86/xen/p2m.c:     vm_area_register_early(&vm, PMD_SIZE *
>> PMDS_PER_MID_PAGE);
>> mm/percpu.c:    vm_area_register_early(&vm, PAGE_SIZE);
>> [wkf@...alhost linux-next]$ git grep vm_area_add_early
>> arch/arm/mm/ioremap.c:  vm_area_add_early(vm);
>> arch/arm64/mm/mmu.c:    vm_area_add_early(vma);
>>
>> x86/alpha won't call vm_area_add_early(), only arm64 could call both vm_area_add_early()
>> and  vm_area_register_early() when this patchset is merged. so it won't break other architectures.
> Thanks for checking.
>
>>> Also, instead of always picking the end, could we search for a range
>>> that fits?
>> We only need a space in vmalloc range,  using end or a range in the middle
>> is not different.
> I was thinking of making it more future-proof in case one registers a
> vm area towards the end of the range. It's fairly easy to pick a range
> in the middle now that you are adding a list traversal.
ok,  will chose a suitable hole in the vmalloc range.
>