Re: [PATCH 05/23] m68k: allow pte_offset_map[_lock]() to fail
Hi Hugh,
On Thu, May 11, 2023 at 4:58 AM Hugh Dickins wrote:
> On Wed, 10 May 2023, Geert Uytterhoeven wrote:
> > On Wed, May 10, 2023 at 6:48 AM Hugh Dickins wrote:
> > > In rare transient cases, not yet made possible, pte_offset_map() and
> > > pte_offset_map_lock() may not find a page table: handle appropriately.
> > >
> > > Restructure cf_tlb_miss() with a pte_unmap() (previously omitted)
> > > at label out, followed by one local_irq_restore() for all.
> >
> > That's a bug fix, which should be a separate patch?
>
> No, that's not a bug fix for the current tree, since m68k does not
> offer CONFIG_HIGHPTE, so pte_unmap() is never anything but a no-op
> for m68k (see include/linux/pgtable.h).
>
> But I want to change pte_unmap() to do something even without
> CONFIG_HIGHPTE, so have to fix up any such previously harmless
> omissions in this series first.
OK.
> > > --- a/arch/m68k/include/asm/mmu_context.h
> > > +++ b/arch/m68k/include/asm/mmu_context.h
> > > @@ -99,7 +99,7 @@ static inline void load_ksp_mmu(struct task_struct
> > > *task)
> > > p4d_t *p4d;
> > > pud_t *pud;
> > > pmd_t *pmd;
> > > - pte_t *pte;
> > > + pte_t *pte = NULL;
> > > unsigned long mmuar;
> > >
> > > local_irq_save(flags);
> > > @@ -139,7 +139,7 @@ static inline void load_ksp_mmu(struct task_struct
> > > *task)
> > >
> > > pte = (mmuar >= PAGE_OFFSET) ? pte_offset_kernel(pmd, mmuar)
> > > : pte_offset_map(pmd, mmuar);
> > > - if (pte_none(*pte) || !pte_present(*pte))
> > > + if (!pte || pte_none(*pte) || !pte_present(*pte))
> > > goto bug;
> >
> > If the absence of a pte is to become a non-abnormal case, it should
> > probably jump to "end" instead, to avoid spamming the kernel log.
>
> I don't think so (but of course it's hard for you to tell, without
> seeing all completed series of series). If pmd_none(*pmd) can safely
> goto bug just above, and pte_none(*pte) goto bug here, well, the !pte
> case is going to be stranger than either of those.
>
> My understanding of this function, load_ksp_mmu(), is that it's dealing
> at context switch with a part of userspace which very much needs to be
> present: whatever keeps that from being swapped out or migrated at
> present, will be sure to keep the !pte case away - we cannot steal its
> page table just at random (and a THP on m68k would be surprising too).
>
> Though there is one case I can think of which will cause !pte here,
> and so goto bug: if the pmd entry has got corrupted, and counts as
> pmd_bad(), which will be tested (and cleared) in pte_offset_map().
> But it is okay to report a bug in that case.
>
> I can certainly change this to goto end instead if you still prefer,
> no problem; but I'd rather keep it as is, if only for me to be proved
> wrong by you actually seeing spam there.
OK, makes sense.
> > > @@ -161,6 +161,8 @@ static inline void load_ksp_mmu(struct task_struct
> > > *task)
> > > bug:
> > > pr_info("ksp load failed: mm=0x%p ksp=0x08%lx\n", mm, mmuar);
> > > end:
> > > + if (pte && mmuar < PAGE_OFFSET)
> > > + pte_unmap(pte);
> >
> > Is this also a bugfix, not mentioned in the patch description?
>
> I'm not sure whether you're referring to the pte_unmap() which we
> already discussed above, or you're seeing something else in addition;
> but I don't think there's a bugfix here, just a rearrangement because
> we now want lots of cases to do the pte_unmap() and local_irq_restore().
I was referring to the addition of pte_unmap().
As per your explanation above, this is not a bugfix.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
Re: [PATCH 05/23] m68k: allow pte_offset_map[_lock]() to fail
On Wed, 10 May 2023, Geert Uytterhoeven wrote:
> Hi Hugh,
>
> Thanks for your patch!
And thank you for looking so quickly, Geert.
>
> On Wed, May 10, 2023 at 6:48 AM Hugh Dickins wrote:
> > In rare transient cases, not yet made possible, pte_offset_map() and
> > pte_offset_map_lock() may not find a page table: handle appropriately.
> >
> > Restructure cf_tlb_miss() with a pte_unmap() (previously omitted)
> > at label out, followed by one local_irq_restore() for all.
>
> That's a bug fix, which should be a separate patch?
No, that's not a bug fix for the current tree, since m68k does not
offer CONFIG_HIGHPTE, so pte_unmap() is never anything but a no-op
for m68k (see include/linux/pgtable.h).
But I want to change pte_unmap() to do something even without
CONFIG_HIGHPTE, so have to fix up any such previously harmless
omissions in this series first.
>
> >
> > Signed-off-by: Hugh Dickins
>
>
> > --- a/arch/m68k/include/asm/mmu_context.h
> > +++ b/arch/m68k/include/asm/mmu_context.h
> > @@ -99,7 +99,7 @@ static inline void load_ksp_mmu(struct task_struct *task)
> > p4d_t *p4d;
> > pud_t *pud;
> > pmd_t *pmd;
> > - pte_t *pte;
> > + pte_t *pte = NULL;
> > unsigned long mmuar;
> >
> > local_irq_save(flags);
> > @@ -139,7 +139,7 @@ static inline void load_ksp_mmu(struct task_struct
> > *task)
> >
> > pte = (mmuar >= PAGE_OFFSET) ? pte_offset_kernel(pmd, mmuar)
> > : pte_offset_map(pmd, mmuar);
> > - if (pte_none(*pte) || !pte_present(*pte))
> > + if (!pte || pte_none(*pte) || !pte_present(*pte))
> > goto bug;
>
> If the absence of a pte is to become a non-abnormal case, it should
> probably jump to "end" instead, to avoid spamming the kernel log.
I don't think so (but of course it's hard for you to tell, without
seeing all completed series of series). If pmd_none(*pmd) can safely
goto bug just above, and pte_none(*pte) goto bug here, well, the !pte
case is going to be stranger than either of those.
My understanding of this function, load_ksp_mmu(), is that it's dealing
at context switch with a part of userspace which very much needs to be
present: whatever keeps that from being swapped out or migrated at
present, will be sure to keep the !pte case away - we cannot steal its
page table just at random (and a THP on m68k would be surprising too).
Though there is one case I can think of which will cause !pte here,
and so goto bug: if the pmd entry has got corrupted, and counts as
pmd_bad(), which will be tested (and cleared) in pte_offset_map().
But it is okay to report a bug in that case.
I can certainly change this to goto end instead if you still prefer,
no problem; but I'd rather keep it as is, if only for me to be proved
wrong by you actually seeing spam there.
>
> >
> > set_pte(pte, pte_mkyoung(*pte));
> > @@ -161,6 +161,8 @@ static inline void load_ksp_mmu(struct task_struct
> > *task)
> > bug:
> > pr_info("ksp load failed: mm=0x%p ksp=0x08%lx\n", mm, mmuar);
> > end:
> > + if (pte && mmuar < PAGE_OFFSET)
> > + pte_unmap(pte);
>
> Is this also a bugfix, not mentioned in the patch description?
I'm not sure whether you're referring to the pte_unmap() which we
already discussed above, or you're seeing something else in addition;
but I don't think there's a bugfix here, just a rearrangement because
we now want lots of cases to do the pte_unmap() and local_irq_restore().
Hugh
>
> > local_irq_restore(flags);
> > }
> >
>
> Gr{oetje,eeting}s,
>
> Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 --
> ge...@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like
> that.
> -- Linus Torvalds
Re: [PATCH 05/23] m68k: allow pte_offset_map[_lock]() to fail
Hi Hugh,
Thanks for your patch!
On Wed, May 10, 2023 at 6:48 AM Hugh Dickins wrote:
> In rare transient cases, not yet made possible, pte_offset_map() and
> pte_offset_map_lock() may not find a page table: handle appropriately.
>
> Restructure cf_tlb_miss() with a pte_unmap() (previously omitted)
> at label out, followed by one local_irq_restore() for all.
That's a bug fix, which should be a separate patch?
>
> Signed-off-by: Hugh Dickins
> --- a/arch/m68k/include/asm/mmu_context.h
> +++ b/arch/m68k/include/asm/mmu_context.h
> @@ -99,7 +99,7 @@ static inline void load_ksp_mmu(struct task_struct *task)
> p4d_t *p4d;
> pud_t *pud;
> pmd_t *pmd;
> - pte_t *pte;
> + pte_t *pte = NULL;
> unsigned long mmuar;
>
> local_irq_save(flags);
> @@ -139,7 +139,7 @@ static inline void load_ksp_mmu(struct task_struct *task)
>
> pte = (mmuar >= PAGE_OFFSET) ? pte_offset_kernel(pmd, mmuar)
> : pte_offset_map(pmd, mmuar);
> - if (pte_none(*pte) || !pte_present(*pte))
> + if (!pte || pte_none(*pte) || !pte_present(*pte))
> goto bug;
If the absence of a pte is to become a non-abnormal case, it should
probably jump to "end" instead, to avoid spamming the kernel log.
>
> set_pte(pte, pte_mkyoung(*pte));
> @@ -161,6 +161,8 @@ static inline void load_ksp_mmu(struct task_struct *task)
> bug:
> pr_info("ksp load failed: mm=0x%p ksp=0x08%lx\n", mm, mmuar);
> end:
> + if (pte && mmuar < PAGE_OFFSET)
> + pte_unmap(pte);
Is this also a bugfix, not mentioned in the patch description?
> local_irq_restore(flags);
> }
>
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
[PATCH 05/23] m68k: allow pte_offset_map[_lock]() to fail
In rare transient cases, not yet made possible, pte_offset_map() and
pte_offset_map_lock() may not find a page table: handle appropriately.
Restructure cf_tlb_miss() with a pte_unmap() (previously omitted)
at label out, followed by one local_irq_restore() for all.
Signed-off-by: Hugh Dickins
---
arch/m68k/include/asm/mmu_context.h | 6 ++--
arch/m68k/kernel/sys_m68k.c | 2 ++
arch/m68k/mm/mcfmmu.c | 52 -
3 files changed, 27 insertions(+), 33 deletions(-)
diff --git a/arch/m68k/include/asm/mmu_context.h
b/arch/m68k/include/asm/mmu_context.h
index 8ed6ac14d99f..141bbdfad960 100644
--- a/arch/m68k/include/asm/mmu_context.h
+++ b/arch/m68k/include/asm/mmu_context.h
@@ -99,7 +99,7 @@ static inline void load_ksp_mmu(struct task_struct *task)
p4d_t *p4d;
pud_t *pud;
pmd_t *pmd;
- pte_t *pte;
+ pte_t *pte = NULL;
unsigned long mmuar;
local_irq_save(flags);
@@ -139,7 +139,7 @@ static inline void load_ksp_mmu(struct task_struct *task)
pte = (mmuar >= PAGE_OFFSET) ? pte_offset_kernel(pmd, mmuar)
: pte_offset_map(pmd, mmuar);
- if (pte_none(*pte) || !pte_present(*pte))
+ if (!pte || pte_none(*pte) || !pte_present(*pte))
goto bug;
set_pte(pte, pte_mkyoung(*pte));
@@ -161,6 +161,8 @@ static inline void load_ksp_mmu(struct task_struct *task)
bug:
pr_info("ksp load failed: mm=0x%p ksp=0x08%lx\n", mm, mmuar);
end:
+ if (pte && mmuar < PAGE_OFFSET)
+ pte_unmap(pte);
local_irq_restore(flags);
}
diff --git a/arch/m68k/kernel/sys_m68k.c b/arch/m68k/kernel/sys_m68k.c
index bd0274c7592e..c586034d2a7a 100644
--- a/arch/m68k/kernel/sys_m68k.c
+++ b/arch/m68k/kernel/sys_m68k.c
@@ -488,6 +488,8 @@ sys_atomic_cmpxchg_32(unsigned long newval, int oldval, int
d3, int d4, int d5,
if (!pmd_present(*pmd))
goto bad_access;
pte = pte_offset_map_lock(mm, pmd, (unsigned long)mem, );
+ if (!pte)
+ goto bad_access;
if (!pte_present(*pte) || !pte_dirty(*pte)
|| !pte_write(*pte)) {
pte_unmap_unlock(pte, ptl);
diff --git a/arch/m68k/mm/mcfmmu.c b/arch/m68k/mm/mcfmmu.c
index 70aa0979e027..42f45abea37a 100644
--- a/arch/m68k/mm/mcfmmu.c
+++ b/arch/m68k/mm/mcfmmu.c
@@ -91,7 +91,8 @@ int cf_tlb_miss(struct pt_regs *regs, int write, int dtlb,
int extension_word)
p4d_t *p4d;
pud_t *pud;
pmd_t *pmd;
- pte_t *pte;
+ pte_t *pte = NULL;
+ int ret = -1;
int asid;
local_irq_save(flags);
@@ -100,47 +101,33 @@ int cf_tlb_miss(struct pt_regs *regs, int write, int
dtlb, int extension_word)
regs->pc + (extension_word * sizeof(long));
mm = (!user_mode(regs) && KMAPAREA(mmuar)) ? _mm : current->mm;
- if (!mm) {
- local_irq_restore(flags);
- return -1;
- }
+ if (!mm)
+ goto out;
pgd = pgd_offset(mm, mmuar);
- if (pgd_none(*pgd)) {
- local_irq_restore(flags);
- return -1;
- }
+ if (pgd_none(*pgd))
+ goto out;
p4d = p4d_offset(pgd, mmuar);
- if (p4d_none(*p4d)) {
- local_irq_restore(flags);
- return -1;
- }
+ if (p4d_none(*p4d))
+ goto out;
pud = pud_offset(p4d, mmuar);
- if (pud_none(*pud)) {
- local_irq_restore(flags);
- return -1;
- }
+ if (pud_none(*pud))
+ goto out;
pmd = pmd_offset(pud, mmuar);
- if (pmd_none(*pmd)) {
- local_irq_restore(flags);
- return -1;
- }
+ if (pmd_none(*pmd))
+ goto out;
pte = (KMAPAREA(mmuar)) ? pte_offset_kernel(pmd, mmuar)
: pte_offset_map(pmd, mmuar);
- if (pte_none(*pte) || !pte_present(*pte)) {
- local_irq_restore(flags);
- return -1;
- }
+ if (!pte || pte_none(*pte) || !pte_present(*pte))
+ goto out;
if (write) {
- if (!pte_write(*pte)) {
- local_irq_restore(flags);
- return -1;
- }
+ if (!pte_write(*pte))
+ goto out;
set_pte(pte, pte_mkdirty(*pte));
}
@@ -161,9 +148,12 @@ int cf_tlb_miss(struct pt_regs *regs, int write, int dtlb,
int extension_word)
mmu_write(MMUOR, MMUOR_ACC | MMUOR_UAA);
else
mmu_write(MMUOR, MMUOR_ITLB | MMUOR_ACC | MMUOR_UAA);
-
+ ret = 0;
+out:
+ if (pte && !KMAPAREA(mmuar))
+ pte_unmap(pte);
local_irq_restore(flags);
- return 0;
+ return ret;
}
void __init
