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Message-ID: <4917e6ac-2874-218c-a3be-f2a1462f11c5@loongson.cn>
Date: Sat, 12 Oct 2024 10:51:22 +0800
From: maobibo <maobibo@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
David Hildenbrand <david@...hat.com>, Barry Song <baohua@...nel.org>,
loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org,
kasan-dev@...glegroups.com, linux-mm@...ck.org
Subject: Re: [PATCH 4/4] LoongArch: Use atomic operation with set_pte and
pte_clear function
Huacai,
On 2024/10/12 上午10:16, Huacai Chen wrote:
> Hi, Bibo,
>
> On Thu, Oct 10, 2024 at 11:50 AM Bibo Mao <maobibo@...ngson.cn> wrote:
>>
>> For kernel space area on LoongArch system, both two consecutive page
>> table entries should be enabled with PAGE_GLOBAL bit. So with function
>> set_pte() and pte_clear(), pte buddy entry is checked and set besides
>> its own pte entry. However it is not atomic operation to set both two
>> pte entries, there is problem with test_vmalloc test case.
>>
>> With previous patch, all page table entries are set with PAGE_GLOBAL
>> bit at beginning. Only its own pte entry need update with function
>> set_pte() and pte_clear(), nothing to do with buddy pte entry.
>>
>> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
>> ---
>> arch/loongarch/include/asm/pgtable.h | 44 ++++++++++------------------
>> 1 file changed, 15 insertions(+), 29 deletions(-)
>>
>> diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
>> index 22e3a8f96213..4be3f0dbecda 100644
>> --- a/arch/loongarch/include/asm/pgtable.h
>> +++ b/arch/loongarch/include/asm/pgtable.h
>> @@ -325,40 +325,26 @@ extern void paging_init(void);
>> static inline void set_pte(pte_t *ptep, pte_t pteval)
>> {
>> WRITE_ONCE(*ptep, pteval);
>> +}
>>
>> - if (pte_val(pteval) & _PAGE_GLOBAL) {
>> - pte_t *buddy = ptep_buddy(ptep);
>> - /*
>> - * Make sure the buddy is global too (if it's !none,
>> - * it better already be global)
>> - */
>> - if (pte_none(ptep_get(buddy))) {
>> -#ifdef CONFIG_SMP
>> - /*
>> - * For SMP, multiple CPUs can race, so we need
>> - * to do this atomically.
>> - */
>> - __asm__ __volatile__(
>> - __AMOR "$zero, %[global], %[buddy] \n"
>> - : [buddy] "+ZB" (buddy->pte)
>> - : [global] "r" (_PAGE_GLOBAL)
>> - : "memory");
>> -
>> - DBAR(0b11000); /* o_wrw = 0b11000 */
>> -#else /* !CONFIG_SMP */
>> - WRITE_ONCE(*buddy, __pte(pte_val(ptep_get(buddy)) | _PAGE_GLOBAL));
>> -#endif /* CONFIG_SMP */
>> - }
>> - }
>> +static inline unsigned long __ptep_get_and_clear(pte_t *ptep)
>> +{
>> + return atomic64_fetch_and(_PAGE_GLOBAL, (atomic64_t *)&pte_val(*ptep));
>> }
>>
>> static inline void pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *ptep)
>> {
>> - /* Preserve global status for the pair */
>> - if (pte_val(ptep_get(ptep_buddy(ptep))) & _PAGE_GLOBAL)
>> - set_pte(ptep, __pte(_PAGE_GLOBAL));
>> - else
>> - set_pte(ptep, __pte(0));
>> + __ptep_get_and_clear(ptep);
> With the first patch, a kernel pte always take _PAGE_GLOBAL, so we
> don't need an expensive atomic operation, just
> "set_pte(pte_val(ptep_get(ptep)) & _PAGE_GLOBAL)" is OK here. And then
> we don't need a custom ptep_get_and_clear().
Will use non-atomic method and test again, also will remove customed
function ptep_get_and_clear().
Regards
Bibo Mao
>
>
> Huacai
>
>> +}
>> +
>> +#define __HAVE_ARCH_PTEP_GET_AND_CLEAR
>> +static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
>> + unsigned long addr, pte_t *ptep)
>> +{
>> + unsigned long val;
>> +
>> + val = __ptep_get_and_clear(ptep);
>> + return __pte(val);
>> }
>>
>> #define PGD_T_LOG2 (__builtin_ffs(sizeof(pgd_t)) - 1)
>> --
>> 2.39.3
>>
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