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Message-ID: <CAAhV-H51W3ZRNxUjeAx52j6Tq18CEhB3_YeSH=psjAbEJUdwgg@mail.gmail.com>
Date: Fri, 18 Oct 2024 14:32:54 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: maobibo <maobibo@...ngson.cn>
Cc: wuruiyang@...ngson.cn, 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 v2 1/3] LoongArch: Set initial pte entry with PAGE_GLOBAL
for kernel space
On Fri, Oct 18, 2024 at 2:23 PM maobibo <maobibo@...ngson.cn> wrote:
>
>
>
> On 2024/10/18 下午12:23, Huacai Chen wrote:
> > On Fri, Oct 18, 2024 at 12:16 PM maobibo <maobibo@...ngson.cn> wrote:
> >>
> >>
> >>
> >> On 2024/10/18 下午12:11, Huacai Chen wrote:
> >>> On Fri, Oct 18, 2024 at 11:44 AM maobibo <maobibo@...ngson.cn> wrote:
> >>>>
> >>>>
> >>>>
> >>>> On 2024/10/18 上午11:14, Huacai Chen wrote:
> >>>>> Hi, Bibo,
> >>>>>
> >>>>> I applied this patch but drop the part of arch/loongarch/mm/kasan_init.c:
> >>>>> https://git.kernel.org/pub/scm/linux/kernel/git/chenhuacai/linux-loongson.git/commit/?h=loongarch-next&id=15832255e84494853f543b4c70ced50afc403067
> >>>>>
> >>>>> Because kernel_pte_init() should operate on page-table pages, not on
> >>>>> data pages. You have already handle page-table page in
> >>>>> mm/kasan/init.c, and if we don't drop the modification on data pages
> >>>>> in arch/loongarch/mm/kasan_init.c, the kernel fail to boot if KASAN is
> >>>>> enabled.
> >>>>>
> >>>> 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 */
> >>>> - }
> >>>> - }
> >>>> + DBAR(0b11000); /* o_wrw = 0b11000 */
> >>>> }
> >>>>
> >>>> No, please hold on. This issue exists about twenty years, Do we need be
> >>>> in such a hurry now?
> >>>>
> >>>> why is DBAR(0b11000) added in set_pte()?
> >>> It exists before, not added by this patch. The reason is explained in
> >>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v6.12-rc3&id=f93f67d06b1023313ef1662eac490e29c025c030
> >> why speculative accesses may cause spurious page fault in kernel space
> >> with PTE enabled? speculative accesses exists anywhere, it does not
> >> cause spurious page fault.
> > Confirmed by Ruiyang Wu, and even if DBAR(0b11000) is wrong, that
> > means another patch's mistake, not this one. This one just keeps the
> > old behavior.
> > +CC Ruiyang Wu here.
> Also from Ruiyang Wu, the information is that speculative accesses may
> insert stale TLB, however no page fault exception.
>
> So adding barrier in set_pte() does not prevent speculative accesses.
> And you write patch here, however do not know the actual reason?
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v6.12-rc3&id=f93f67d06b1023313ef1662eac490e29c025c030
I have CCed Ruiyang, whether the description is correct can be judged by him.
Huacai
>
> Bibo Mao
> >
> > Huacai
> >
> >>
> >> Obvious you do not it and you write wrong patch.
> >>
> >>>
> >>> Huacai
> >>>
> >>>>
> >>>> Regards
> >>>> Bibo Mao
> >>>>> Huacai
> >>>>>
> >>>>> On Mon, Oct 14, 2024 at 11:59 AM Bibo Mao <maobibo@...ngson.cn> wrote:
> >>>>>>
> >>>>>> Unlike general architectures, there are two pages in one TLB entry
> >>>>>> on LoongArch system. For kernel space, it requires both two pte
> >>>>>> entries with PAGE_GLOBAL bit set, else HW treats it as non-global
> >>>>>> tlb, there will be potential problems if tlb entry for kernel space
> >>>>>> is not global. Such as fail to flush kernel tlb with function
> >>>>>> local_flush_tlb_kernel_range() which only flush tlb with global bit.
> >>>>>>
> >>>>>> With function kernel_pte_init() added, it can be used to init pte
> >>>>>> table when it is created for kernel address space, and the default
> >>>>>> initial pte value is PAGE_GLOBAL rather than zero at beginning.
> >>>>>>
> >>>>>> Kernel address space areas includes fixmap, percpu, vmalloc, kasan
> >>>>>> and vmemmap areas set default pte entry with PAGE_GLOBAL set.
> >>>>>>
> >>>>>> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
> >>>>>> ---
> >>>>>> arch/loongarch/include/asm/pgalloc.h | 13 +++++++++++++
> >>>>>> arch/loongarch/include/asm/pgtable.h | 1 +
> >>>>>> arch/loongarch/mm/init.c | 4 +++-
> >>>>>> arch/loongarch/mm/kasan_init.c | 4 +++-
> >>>>>> arch/loongarch/mm/pgtable.c | 22 ++++++++++++++++++++++
> >>>>>> include/linux/mm.h | 1 +
> >>>>>> mm/kasan/init.c | 8 +++++++-
> >>>>>> mm/sparse-vmemmap.c | 5 +++++
> >>>>>> 8 files changed, 55 insertions(+), 3 deletions(-)
> >>>>>>
> >>>>>> diff --git a/arch/loongarch/include/asm/pgalloc.h b/arch/loongarch/include/asm/pgalloc.h
> >>>>>> index 4e2d6b7ca2ee..b2698c03dc2c 100644
> >>>>>> --- a/arch/loongarch/include/asm/pgalloc.h
> >>>>>> +++ b/arch/loongarch/include/asm/pgalloc.h
> >>>>>> @@ -10,8 +10,21 @@
> >>>>>>
> >>>>>> #define __HAVE_ARCH_PMD_ALLOC_ONE
> >>>>>> #define __HAVE_ARCH_PUD_ALLOC_ONE
> >>>>>> +#define __HAVE_ARCH_PTE_ALLOC_ONE_KERNEL
> >>>>>> #include <asm-generic/pgalloc.h>
> >>>>>>
> >>>>>> +static inline pte_t *pte_alloc_one_kernel(struct mm_struct *mm)
> >>>>>> +{
> >>>>>> + pte_t *pte;
> >>>>>> +
> >>>>>> + pte = (pte_t *) __get_free_page(GFP_KERNEL);
> >>>>>> + if (!pte)
> >>>>>> + return NULL;
> >>>>>> +
> >>>>>> + kernel_pte_init(pte);
> >>>>>> + return pte;
> >>>>>> +}
> >>>>>> +
> >>>>>> static inline void pmd_populate_kernel(struct mm_struct *mm,
> >>>>>> pmd_t *pmd, pte_t *pte)
> >>>>>> {
> >>>>>> diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
> >>>>>> index 9965f52ef65b..22e3a8f96213 100644
> >>>>>> --- a/arch/loongarch/include/asm/pgtable.h
> >>>>>> +++ b/arch/loongarch/include/asm/pgtable.h
> >>>>>> @@ -269,6 +269,7 @@ extern void set_pmd_at(struct mm_struct *mm, unsigned long addr, pmd_t *pmdp, pm
> >>>>>> extern void pgd_init(void *addr);
> >>>>>> extern void pud_init(void *addr);
> >>>>>> extern void pmd_init(void *addr);
> >>>>>> +extern void kernel_pte_init(void *addr);
> >>>>>>
> >>>>>> /*
> >>>>>> * Encode/decode swap entries and swap PTEs. Swap PTEs are all PTEs that
> >>>>>> diff --git a/arch/loongarch/mm/init.c b/arch/loongarch/mm/init.c
> >>>>>> index 8a87a482c8f4..9f26e933a8a3 100644
> >>>>>> --- a/arch/loongarch/mm/init.c
> >>>>>> +++ b/arch/loongarch/mm/init.c
> >>>>>> @@ -198,9 +198,11 @@ pte_t * __init populate_kernel_pte(unsigned long addr)
> >>>>>> if (!pmd_present(pmdp_get(pmd))) {
> >>>>>> pte_t *pte;
> >>>>>>
> >>>>>> - pte = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
> >>>>>> + pte = memblock_alloc_raw(PAGE_SIZE, PAGE_SIZE);
> >>>>>> if (!pte)
> >>>>>> panic("%s: Failed to allocate memory\n", __func__);
> >>>>>> +
> >>>>>> + kernel_pte_init(pte);
> >>>>>> pmd_populate_kernel(&init_mm, pmd, pte);
> >>>>>> }
> >>>>>>
> >>>>>> diff --git a/arch/loongarch/mm/kasan_init.c b/arch/loongarch/mm/kasan_init.c
> >>>>>> index 427d6b1aec09..34988573b0d5 100644
> >>>>>> --- a/arch/loongarch/mm/kasan_init.c
> >>>>>> +++ b/arch/loongarch/mm/kasan_init.c
> >>>>>> @@ -152,6 +152,8 @@ static void __init kasan_pte_populate(pmd_t *pmdp, unsigned long addr,
> >>>>>> phys_addr_t page_phys = early ?
> >>>>>> __pa_symbol(kasan_early_shadow_page)
> >>>>>> : kasan_alloc_zeroed_page(node);
> >>>>>> + if (!early)
> >>>>>> + kernel_pte_init(__va(page_phys));
> >>>>>> next = addr + PAGE_SIZE;
> >>>>>> set_pte(ptep, pfn_pte(__phys_to_pfn(page_phys), PAGE_KERNEL));
> >>>>>> } while (ptep++, addr = next, addr != end && __pte_none(early, ptep_get(ptep)));
> >>>>>> @@ -287,7 +289,7 @@ void __init kasan_init(void)
> >>>>>> set_pte(&kasan_early_shadow_pte[i],
> >>>>>> pfn_pte(__phys_to_pfn(__pa_symbol(kasan_early_shadow_page)), PAGE_KERNEL_RO));
> >>>>>>
> >>>>>> - memset(kasan_early_shadow_page, 0, PAGE_SIZE);
> >>>>>> + kernel_pte_init(kasan_early_shadow_page);
> >>>>>> csr_write64(__pa_symbol(swapper_pg_dir), LOONGARCH_CSR_PGDH);
> >>>>>> local_flush_tlb_all();
> >>>>>>
> >>>>>> diff --git a/arch/loongarch/mm/pgtable.c b/arch/loongarch/mm/pgtable.c
> >>>>>> index eb6a29b491a7..228ffc1db0a3 100644
> >>>>>> --- a/arch/loongarch/mm/pgtable.c
> >>>>>> +++ b/arch/loongarch/mm/pgtable.c
> >>>>>> @@ -38,6 +38,28 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
> >>>>>> }
> >>>>>> EXPORT_SYMBOL_GPL(pgd_alloc);
> >>>>>>
> >>>>>> +void kernel_pte_init(void *addr)
> >>>>>> +{
> >>>>>> + unsigned long *p, *end;
> >>>>>> + unsigned long entry;
> >>>>>> +
> >>>>>> + entry = (unsigned long)_PAGE_GLOBAL;
> >>>>>> + p = (unsigned long *)addr;
> >>>>>> + end = p + PTRS_PER_PTE;
> >>>>>> +
> >>>>>> + do {
> >>>>>> + p[0] = entry;
> >>>>>> + p[1] = entry;
> >>>>>> + p[2] = entry;
> >>>>>> + p[3] = entry;
> >>>>>> + p[4] = entry;
> >>>>>> + p += 8;
> >>>>>> + p[-3] = entry;
> >>>>>> + p[-2] = entry;
> >>>>>> + p[-1] = entry;
> >>>>>> + } while (p != end);
> >>>>>> +}
> >>>>>> +
> >>>>>> void pgd_init(void *addr)
> >>>>>> {
> >>>>>> unsigned long *p, *end;
> >>>>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
> >>>>>> index ecf63d2b0582..6909fe059a2c 100644
> >>>>>> --- a/include/linux/mm.h
> >>>>>> +++ b/include/linux/mm.h
> >>>>>> @@ -3818,6 +3818,7 @@ void *sparse_buffer_alloc(unsigned long size);
> >>>>>> struct page * __populate_section_memmap(unsigned long pfn,
> >>>>>> unsigned long nr_pages, int nid, struct vmem_altmap *altmap,
> >>>>>> struct dev_pagemap *pgmap);
> >>>>>> +void kernel_pte_init(void *addr);
> >>>>>> void pmd_init(void *addr);
> >>>>>> void pud_init(void *addr);
> >>>>>> pgd_t *vmemmap_pgd_populate(unsigned long addr, int node);
> >>>>>> diff --git a/mm/kasan/init.c b/mm/kasan/init.c
> >>>>>> index 89895f38f722..ac607c306292 100644
> >>>>>> --- a/mm/kasan/init.c
> >>>>>> +++ b/mm/kasan/init.c
> >>>>>> @@ -106,6 +106,10 @@ static void __ref zero_pte_populate(pmd_t *pmd, unsigned long addr,
> >>>>>> }
> >>>>>> }
> >>>>>>
> >>>>>> +void __weak __meminit kernel_pte_init(void *addr)
> >>>>>> +{
> >>>>>> +}
> >>>>>> +
> >>>>>> static int __ref zero_pmd_populate(pud_t *pud, unsigned long addr,
> >>>>>> unsigned long end)
> >>>>>> {
> >>>>>> @@ -126,8 +130,10 @@ static int __ref zero_pmd_populate(pud_t *pud, unsigned long addr,
> >>>>>>
> >>>>>> if (slab_is_available())
> >>>>>> p = pte_alloc_one_kernel(&init_mm);
> >>>>>> - else
> >>>>>> + else {
> >>>>>> p = early_alloc(PAGE_SIZE, NUMA_NO_NODE);
> >>>>>> + kernel_pte_init(p);
> >>>>>> + }
> >>>>>> if (!p)
> >>>>>> return -ENOMEM;
> >>>>>>
> >>>>>> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> >>>>>> index edcc7a6b0f6f..c0388b2e959d 100644
> >>>>>> --- a/mm/sparse-vmemmap.c
> >>>>>> +++ b/mm/sparse-vmemmap.c
> >>>>>> @@ -184,6 +184,10 @@ static void * __meminit vmemmap_alloc_block_zero(unsigned long size, int node)
> >>>>>> return p;
> >>>>>> }
> >>>>>>
> >>>>>> +void __weak __meminit kernel_pte_init(void *addr)
> >>>>>> +{
> >>>>>> +}
> >>>>>> +
> >>>>>> pmd_t * __meminit vmemmap_pmd_populate(pud_t *pud, unsigned long addr, int node)
> >>>>>> {
> >>>>>> pmd_t *pmd = pmd_offset(pud, addr);
> >>>>>> @@ -191,6 +195,7 @@ pmd_t * __meminit vmemmap_pmd_populate(pud_t *pud, unsigned long addr, int node)
> >>>>>> void *p = vmemmap_alloc_block_zero(PAGE_SIZE, node);
> >>>>>> if (!p)
> >>>>>> return NULL;
> >>>>>> + kernel_pte_init(p);
> >>>>>> pmd_populate_kernel(&init_mm, pmd, p);
> >>>>>> }
> >>>>>> return pmd;
> >>>>>> --
> >>>>>> 2.39.3
> >>>>>>
> >>>>
> >>>>
> >>
> >>
>
>
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