On Tue, Oct 08, 2019 at 12:58:57PM +0000, Justin He (Arm Technology China) wrote: > Hi Will > > > -----Original Message----- > > From: Will Deacon <[email protected]> > > Sent: 2019年10月8日 20:40 > > To: Justin He (Arm Technology China) <[email protected]> > > Cc: Catalin Marinas <[email protected]>; Mark Rutland > > <[email protected]>; James Morse <[email protected]>; Marc > > Zyngier <[email protected]>; Matthew Wilcox <[email protected]>; Kirill A. > > Shutemov <[email protected]>; linux-arm- > > [email protected]; [email protected]; linux- > > [email protected]; Punit Agrawal <[email protected]>; Thomas > > Gleixner <[email protected]>; Andrew Morton <akpm@linux- > > foundation.org>; [email protected]; Kaly Xin (Arm Technology China) > > <[email protected]>; nd <[email protected]> > > Subject: Re: [PATCH v10 3/3] mm: fix double page fault on arm64 if PTE_AF > > is cleared > > > > On Tue, Oct 08, 2019 at 02:19:05AM +0000, Justin He (Arm Technology > > China) wrote: > > > > -----Original Message----- > > > > From: Will Deacon <[email protected]> > > > > Sent: 2019年10月1日 20:54 > > > > To: Justin He (Arm Technology China) <[email protected]> > > > > Cc: Catalin Marinas <[email protected]>; Mark Rutland > > > > <[email protected]>; James Morse <[email protected]>; > > Marc > > > > Zyngier <[email protected]>; Matthew Wilcox <[email protected]>; > > Kirill A. > > > > Shutemov <[email protected]>; linux-arm- > > > > [email protected]; [email protected]; linux- > > > > [email protected]; Punit Agrawal <[email protected]>; Thomas > > > > Gleixner <[email protected]>; Andrew Morton <akpm@linux- > > > > foundation.org>; [email protected]; Kaly Xin (Arm Technology China) > > > > <[email protected]> > > > > Subject: Re: [PATCH v10 3/3] mm: fix double page fault on arm64 if > > PTE_AF > > > > is cleared > > > > > > > > On Mon, Sep 30, 2019 at 09:57:40AM +0800, Jia He wrote: > > > > > diff --git a/mm/memory.c b/mm/memory.c > > > > > index b1ca51a079f2..1f56b0118ef5 100644 > > > > > --- a/mm/memory.c > > > > > +++ b/mm/memory.c > > > > > @@ -118,6 +118,13 @@ int randomize_va_space __read_mostly = > > > > > 2; > > > > > #endif > > > > > > > > > > +#ifndef arch_faults_on_old_pte > > > > > +static inline bool arch_faults_on_old_pte(void) > > > > > +{ > > > > > + return false; > > > > > +} > > > > > +#endif > > > > > > > > Kirill has acked this, so I'm happy to take the patch as-is, however > > > > isn't > > > > it the case that /most/ architectures will want to return true for > > > > arch_faults_on_old_pte()? In which case, wouldn't it make more sense > > for > > > > that to be the default, and have x86 and arm64 provide an override? > > For > > > > example, aren't most architectures still going to hit the double fault > > > > scenario even with your patch applied? > > > > > > No, after applying my patch series, only those architectures which don't > > provide > > > setting access flag by hardware AND don't implement their > > arch_faults_on_old_pte > > > will hit the double page fault. > > > > > > The meaning of true for arch_faults_on_old_pte() is "this arch doesn't > > have the hardware > > > setting access flag way, it might cause page fault on an old pte" > > > I don't want to change other architectures' default behavior here. So by > > default, > > > arch_faults_on_old_pte() is false. > > > > ...and my complaint is that this is the majority of supported architectures, > > so you're fixing something for arm64 which also affects arm, powerpc, > > alpha, mips, riscv, ... > > So, IIUC, you suggested that: > 1. by default, arch_faults_on_old_pte() return true > 2. on X86, let arch_faults_on_old_pte() be overrided as returning false > 3. on arm64, let it be as-is my patch set. > 4. let other architectures decide the behavior. (But by default, it will set > pte_young) > > I am ok with that if no objections from others. > > @Kirill A. Shutemov Do you have any comments? Thanks
Sounds sane to me. -- Kirill A. Shutemov
