Re: [RFCv2 08/10] x86/mm: Make LAM_U48 and mappings above 47-bits mutually exclusive

Kirill A. Shutemov
2022-05-18T17:28:51Z

On Wed, May 18, 2022 at 02:13:06PM +0530, Bharata B Rao wrote:
> On 5/11/2022 7:57 AM, Kirill A. Shutemov wrote:
> > LAM_U48 steals bits above 47-bit for tags and makes it impossible for
> > userspace to use full address space on 5-level paging machine.
> >
> > Make these features mutually exclusive: whichever gets enabled first
> > blocks the othe one.
> >
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > ---
> > arch/x86/include/asm/elf.h | 3 ++-
> > arch/x86/include/asm/mmu_context.h | 13 +++++++++++++
> > arch/x86/kernel/sys_x86_64.c | 5 +++--
> > arch/x86/mm/hugetlbpage.c | 6 ++++--
> > arch/x86/mm/mmap.c | 9 ++++++++-
> > 5 files changed, 30 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
> > index 29fea180a665..53b96b0c8cc3 100644
> > --- a/arch/x86/include/asm/elf.h
> > +++ b/arch/x86/include/asm/elf.h
> > @@ -328,7 +328,8 @@ static inline int mmap_is_ia32(void)
> > extern unsigned long task_size_32bit(void);
> > extern unsigned long task_size_64bit(int full_addr_space);
> > extern unsigned long get_mmap_base(int is_legacy);
> > -extern bool mmap_address_hint_valid(unsigned long addr, unsigned long len);
> > +extern bool mmap_address_hint_valid(struct mm_struct *mm,
> > + unsigned long addr, unsigned long len);
> > extern unsigned long get_sigframe_size(void);
> >
> > #ifdef CONFIG_X86_32
> > diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
> > index 27516046117a..c8a6d80dfec3 100644
> > --- a/arch/x86/include/asm/mmu_context.h
> > +++ b/arch/x86/include/asm/mmu_context.h
> > @@ -218,6 +218,19 @@ static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
> >
> > unsigned long __get_current_cr3_fast(void);
> >
> > +#ifdef CONFIG_X86_5LEVEL
> > +static inline bool full_va_allowed(struct mm_struct *mm)
> > +{
> > + /* LAM_U48 steals VA bits abouve 47-bit for tags */
> > + return mm->context.lam != LAM_U48;
> > +}
> > +#else
>
> This is called from X86 common code but appears to be LAM-specific.
> What would mm->context.lam contain if X86_FEATURE_LAM isn't set?

0. So full_va_allowed() will always return true.

--
Kirill A. Shutemov