Re: [PATCH v2 2/3] arm64: mm: HVO: support BBM of vmemmap pgtable safely

[Nanyong Sun]

On 2023/12/20 14:32, Muchun Song wrote:

> > On Dec 20, 2023, at 13:18, Nanyong Sun <sunnanyong@xxxxxxxxxx> wrote:
> >
> > Implement vmemmap_update_pmd and vmemmap_update_pte on arm64 to do
> > BBM(break-before-make) logic when change the page table of vmemmap
> > address, they will under the init_mm.page_table_lock.
> > If a translation fault of vmemmap address concurrently happened after
> > pte/pmd cleared, vmemmap page fault handler will acquire the
> > init_mm.page_table_lock to wait for vmemmap update to complete,
> > by then the virtual address is valid again, so PF can return and
> > access can continue.
> > In other case, do the traditional kernel fault.
> >
> > Implement vmemmap_flush_tlb_all/range on arm64 with nothing
> > to do because tlb already flushed in every single BBM.
> >
> > Signed-off-by: Nanyong Sun <sunnanyong@xxxxxxxxxx>
> > ---
> > arch/arm64/include/asm/esr.h |  4 ++
> > arch/arm64/include/asm/mmu.h | 20 +++++++++
> > arch/arm64/mm/fault.c        | 78 ++++++++++++++++++++++++++++++++++--
> > arch/arm64/mm/mmu.c          | 28 +++++++++++++
> > 4 files changed, 127 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
> > index ae35939f395b..1c63256efd25 100644
> > --- a/arch/arm64/include/asm/esr.h
> > +++ b/arch/arm64/include/asm/esr.h
> > @@ -116,6 +116,10 @@
> > #define ESR_ELx_FSC_SERROR (0x11)
> > #define ESR_ELx_FSC_ACCESS (0x08)
> > #define ESR_ELx_FSC_FAULT (0x04)
> > +#define ESR_ELx_FSC_FAULT_L0    (0x04)
> > +#define ESR_ELx_FSC_FAULT_L1    (0x05)
> > +#define ESR_ELx_FSC_FAULT_L2    (0x06)
> > +#define ESR_ELx_FSC_FAULT_L3    (0x07)
> > #define ESR_ELx_FSC_PERM (0x0C)
> > #define ESR_ELx_FSC_SEA_TTW0 (0x14)
> > #define ESR_ELx_FSC_SEA_TTW1 (0x15)
> > diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
> > index 2fcf51231d6e..b553bc37c925 100644
> > --- a/arch/arm64/include/asm/mmu.h
> > +++ b/arch/arm64/include/asm/mmu.h
> > @@ -76,5 +76,25 @@ extern bool kaslr_requires_kpti(void);
> > #define INIT_MM_CONTEXT(name) \
> > .pgd = init_pg_dir,
> >
> > +#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
> > +void vmemmap_update_pmd(unsigned long addr, pmd_t *pmdp, pte_t *ptep);
> > +#define vmemmap_update_pmd vmemmap_update_pmd
> > +void vmemmap_update_pte(unsigned long addr, pte_t *ptep, pte_t pte);
> > +#define vmemmap_update_pte vmemmap_update_pte
> > +
> > +static inline void vmemmap_flush_tlb_all(void)
> > +{
> > + 	/* do nothing, already flushed tlb in every single BBM */
> > +}
> > +#define vmemmap_flush_tlb_all vmemmap_flush_tlb_all
> > +
> > +static inline void vmemmap_flush_tlb_range(unsigned long start,
> > +   unsigned long end)
> > +{
> > + 	/* do nothing, already flushed tlb in every single BBM */
> > +}
> > +#define vmemmap_flush_tlb_range vmemmap_flush_tlb_range
> > +#endif
> I think those declaration related to TLB flushing should be moved
> to arch/arm64/include/asm/tlbflush.h since we do not include
> <asm/mmu.h> explicitly in hugetlb_vmemmap.c and its functionality
> is to flush TLB. Luckily, <asm/tlbflush.h> is included by hugetlb_vmemmap.c.
>
> Additionally, vmemmap_update_pmd/pte helpers should be moved to
> arch/arm64/include/asm/pgtable.h since it is really pgtable related
> operations.
>
> Thanks.

Yes，I will move them in next version.

Thanks for your time.

> .