Re: [PATCH] MIPS: make userspace mapping young by default

Andrew Morton
2021-02-05T23:41:10Z

On Thu, 4 Feb 2021 16:22:39 +0100 Thomas Bogendoerfer <tsbogend@alpha.franken.de> wrote:

> On Thu, Feb 04, 2021 at 09:39:42AM +0800, Huang Pei wrote:
> > MIPS page fault path(except huge page) takes 3 exceptions (1 TLB Miss
> > + 2 TLB Invalid), butthe second TLB Invalid exception is just
> > triggered by __update_tlb from do_page_fault writing tlb without
> > _PAGE_VALID set. With this patch, user space mapping prot is made
> > young by default (with both _PAGE_VALID and _PAGE_YOUNG set),
> > and it only take 1 TLB Miss + 1 TLB Invalid exception
> >
> > Remove pte_sw_mkyoung without polluting MM code and make page fault
> > delay of MIPS on par with other architecture
> >
> > Signed-off-by: Huang Pei <huangpei@loongson.cn>
> > ---
> > arch/mips/mm/cache.c | 30 ++++++++++++++++--------------
> > include/linux/pgtable.h | 8 --------
> > mm/memory.c | 3 ---
> > 3 files changed, 16 insertions(+), 25 deletions(-)
>
> Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
>
> Andrew, can you take this patch through your tree ?

Sure. I'll drop Christophe's "mm/memory.c: remove pte_sw_mkyoung()"
(https://lkml.kernel.org/r/f302ef92c48d1f08a0459aaee1c568ca11213814.1612345700.git.christophe.leroy@csgroup.eu)
in favour of this one.

I changed this patch a bit due to other changes in -next. Please check
do_set_pte().

From: Huang Pei <huangpei@loongson.cn>
Subject: MIPS: make userspace mapping young by default

MIPS page fault path(except huge page) takes 3 exceptions (1 TLB Miss + 2
TLB Invalid), butthe second TLB Invalid exception is just triggered by
__update_tlb from do_page_fault writing tlb without _PAGE_VALID set. With
this patch, user space mapping prot is made young by default (with both
_PAGE_VALID and _PAGE_YOUNG set), and it only take 1 TLB Miss + 1 TLB
Invalid exception

Remove pte_sw_mkyoung without polluting MM code and make page fault delay
of MIPS on par with other architecture

Link: https://lkml.kernel.org/r/20210204013942.8398-1-huangpei@loongson.cn
Signed-off-by: Huang Pei <huangpei@loongson.cn>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Acked-by: <huangpei@loongson.cn>
Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: <ambrosehua@gmail.com>
Cc: Bibo Mao <maobibo@loongson.cn>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Paul Burton <paulburton@kernel.org>
Cc: Li Xuefeng <lixuefeng@loongson.cn>
Cc: Yang Tiezhu <yangtiezhu@loongson.cn>
Cc: Gao Juxin <gaojuxin@loongson.cn>
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

arch/mips/mm/cache.c | 30 ++++++++++++++++--------------
include/linux/pgtable.h | 8 --------
mm/memory.c | 4 ----
3 files changed, 16 insertions(+), 26 deletions(-)

--- a/arch/mips/mm/cache.c~mips-make-userspace-mapping-young-by-default
+++ a/arch/mips/mm/cache.c
@@ -157,29 +157,31 @@ unsigned long _page_cachable_default;
EXPORT_SYMBOL(_page_cachable_default);

#define PM(p) __pgprot(_page_cachable_default | (p))
+#define PVA(p) PM(_PAGE_VALID | _PAGE_ACCESSED | (p))

static inline void setup_protection_map(void)
{
protection_map[0] = PM(_PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_NO_READ);
- protection_map[1] = PM(_PAGE_PRESENT | _PAGE_NO_EXEC);
- protection_map[2] = PM(_PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_NO_READ);
- protection_map[3] = PM(_PAGE_PRESENT | _PAGE_NO_EXEC);
- protection_map[4] = PM(_PAGE_PRESENT);
- protection_map[5] = PM(_PAGE_PRESENT);
- protection_map[6] = PM(_PAGE_PRESENT);
- protection_map[7] = PM(_PAGE_PRESENT);
+ protection_map[1] = PVA(_PAGE_PRESENT | _PAGE_NO_EXEC);
+ protection_map[2] = PVA(_PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_NO_READ);
+ protection_map[3] = PVA(_PAGE_PRESENT | _PAGE_NO_EXEC);
+ protection_map[4] = PVA(_PAGE_PRESENT);
+ protection_map[5] = PVA(_PAGE_PRESENT);
+ protection_map[6] = PVA(_PAGE_PRESENT);
+ protection_map[7] = PVA(_PAGE_PRESENT);

protection_map[8] = PM(_PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_NO_READ);
- protection_map[9] = PM(_PAGE_PRESENT | _PAGE_NO_EXEC);
- protection_map[10] = PM(_PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_WRITE |
+ protection_map[9] = PVA(_PAGE_PRESENT | _PAGE_NO_EXEC);
+ protection_map[10] = PVA(_PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_WRITE |
_PAGE_NO_READ);
- protection_map[11] = PM(_PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_WRITE);
- protection_map[12] = PM(_PAGE_PRESENT);
- protection_map[13] = PM(_PAGE_PRESENT);
- protection_map[14] = PM(_PAGE_PRESENT | _PAGE_WRITE);
- protection_map[15] = PM(_PAGE_PRESENT | _PAGE_WRITE);
+ protection_map[11] = PVA(_PAGE_PRESENT | _PAGE_NO_EXEC | _PAGE_WRITE);
+ protection_map[12] = PVA(_PAGE_PRESENT);
+ protection_map[13] = PVA(_PAGE_PRESENT);
+ protection_map[14] = PVA(_PAGE_PRESENT);
+ protection_map[15] = PVA(_PAGE_PRESENT);
}

+#undef _PVA
#undef PM

void cpu_cache_init(void)
--- a/include/linux/pgtable.h~mips-make-userspace-mapping-young-by-default
+++ a/include/linux/pgtable.h
@@ -432,14 +432,6 @@ static inline void ptep_set_wrprotect(st
* To be differentiate with macro pte_mkyoung, this macro is used on platforms
* where software maintains page access bit.
*/
-#ifndef pte_sw_mkyoung
-static inline pte_t pte_sw_mkyoung(pte_t pte)
-{
- return pte;
-}
-#define pte_sw_mkyoung pte_sw_mkyoung
-#endif
-
#ifndef pte_savedwrite
#define pte_savedwrite pte_write
#endif
--- a/mm/memory.c~mips-make-userspace-mapping-young-by-default
+++ a/mm/memory.c
@@ -2902,7 +2902,6 @@ static vm_fault_t wp_page_copy(struct vm
}
flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
entry = mk_pte(new_page, vma->vm_page_prot);
- entry = pte_sw_mkyoung(entry);
entry = maybe_mkwrite(pte_mkdirty(entry), vma);

/*
@@ -3560,7 +3559,6 @@ static vm_fault_t do_anonymous_page(stru
__SetPageUptodate(page);

entry = mk_pte(page, vma->vm_page_prot);
- entry = pte_sw_mkyoung(entry);
if (vma->vm_flags & VM_WRITE)
entry = pte_mkwrite(pte_mkdirty(entry));

@@ -3745,8 +3743,6 @@ void do_set_pte(struct vm_fault *vmf, st

if (prefault && arch_wants_old_prefaulted_pte())
entry = pte_mkold(entry);
- else
- entry = pte_sw_mkyoung(entry);

if (write)
entry = maybe_mkwrite(pte_mkdirty(entry), vma);
_