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Re: [Xen-devel] [PATCH v3 07/10] xen/arm: Add handling write fault for dirty-page tracing



On Thu, 1 Aug 2013, Jaeyong Yoo wrote:
> Add handling write fault in do_trap_data_abort_guest for dirty-page tracing.
> Rather than maintaining a bitmap for dirty pages, we use the avail bit in p2m 
> entry.
> For locating the write fault pte in guest p2m, we use virtual-linear page 
> table
> that slots guest p2m into xen's virtual memory.
> 
> Signed-off-by: Jaeyong Yoo <jaeyong.yoo@xxxxxxxxxxx>

Looks good to me.
I would appreciated some more comments in the code to explain the
inner working of the vlp2m.
Nonetheless:

Reviewed-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>


>  xen/arch/arm/mm.c               | 110 
> +++++++++++++++++++++++++++++++++++++++-
>  xen/arch/arm/traps.c            |  16 +++++-
>  xen/include/asm-arm/domain.h    |  11 ++++
>  xen/include/asm-arm/mm.h        |   5 ++
>  xen/include/asm-arm/processor.h |   2 +
>  5 files changed, 142 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index 9d5d3e0..a24afe6 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -680,7 +680,6 @@ void destroy_xen_mappings(unsigned long v, unsigned long 
> e)
>      create_xen_entries(REMOVE, v, 0, (e - v) >> PAGE_SHIFT, 0);
>  }
>  
> -enum mg { mg_clear, mg_ro, mg_rw, mg_rx };
>  static void set_pte_flags_on_range(const char *p, unsigned long l, enum mg 
> mg)
>  {
>      lpae_t pte;
> @@ -1214,6 +1213,115 @@ int is_iomem_page(unsigned long mfn)
>          return 1;
>      return 0;
>  }
> +
> +static uint64_t find_guest_p2m_mfn(struct domain *d, paddr_t addr)
> +{
> +    lpae_t *first = NULL, *second = NULL;
> +    struct p2m_domain *p2m = &d->arch.p2m;
> +    uint64_t mfn = -EFAULT;
> +
> +    if ( first_table_offset(addr) >= LPAE_ENTRIES )
> +        return mfn;
> +
> +    first = __map_domain_page(p2m->first_level);
> +
> +    if ( !first ||
> +         !first[first_table_offset(addr)].walk.valid ||
> +         !first[first_table_offset(addr)].walk.table )
> +        goto done;
> +
> +    second = map_domain_page(first[first_table_offset(addr)].walk.base);
> +
> +    if ( !second ||
> +         !second[second_table_offset(addr)].walk.valid ||
> +         !second[second_table_offset(addr)].walk.table )
> +        goto done;
> +
> +    mfn = second[second_table_offset(addr)].walk.base;
> +
> +done:
> +    if ( second ) unmap_domain_page(second);
> +    if ( first ) unmap_domain_page(first);
> +
> +    return mfn;
> +}
> +
> +/*
> + * routine for dirty-page tracing
> + *
> + * On first write, it page faults, its entry is changed to read-write,
> + * and on retry the write succeeds.
> + *
> + * for locating p2m of the faulting entry, we use virtual-linear page table.
> + */
> +int handle_page_fault(struct domain *d, paddr_t addr)
> +{
> +    int rc = 0;
> +    struct p2m_domain *p2m = &d->arch.p2m;
> +    uint64_t gma_start;
> +    int gma_third_index;
> +    int xen_second_linear, xen_third_table;
> +    lpae_t *xen_third;
> +    lpae_t *vlp2m_pte;
> +
> +    BUG_ON( !d->arch.map_domain.nr_banks );
> +
> +    gma_start = d->arch.map_domain.bank[0].start;
> +    gma_third_index = third_linear_offset(addr - gma_start);
> +    vlp2m_pte = (lpae_t *)(d->arch.dirty.vlpt_start +
> +                           sizeof(lpae_t) * gma_third_index);
> +
> +    BUG_ON( (void *)vlp2m_pte > d->arch.dirty.vlpt_end );
> +
> +    spin_lock(&p2m->lock);
> +
> +    xen_second_linear = second_linear_offset((unsigned long)vlp2m_pte);
> +    xen_third_table = third_table_offset((unsigned long)vlp2m_pte);
> +
> +    /* starting from xen second level page table */
> +    if ( !xen_second[xen_second_linear].pt.valid )
> +    {
> +        unsigned long va = (unsigned long)vlp2m_pte & ~(PAGE_SIZE-1);
> +
> +        rc = create_xen_table(&xen_second[second_linear_offset(va)]);
> +        if ( rc < 0 )
> +            goto out;
> +    }
> +
> +    BUG_ON( !xen_second[xen_second_linear].pt.valid );
> +
> +    /* at this point, xen second level pt has valid entry
> +     * check again the validity of third level pt */
> +    xen_third = __va(pfn_to_paddr(xen_second[xen_second_linear].pt.base));
> +
> +    /* xen third-level page table invalid */
> +    if ( !xen_third[xen_third_table].p2m.valid )
> +    {
> +        uint64_t mfn = find_guest_p2m_mfn(d, addr);
> +        lpae_t pte = mfn_to_xen_entry(mfn);
> +        unsigned long va = (unsigned long)vlp2m_pte & ~(PAGE_SIZE-1);
> +
> +        pte.pt.table = 1; /* 4k mappings always have this bit set */
> +        write_pte(&xen_third[xen_third_table], pte);
> +        flush_xen_data_tlb_range_va(va, PAGE_SIZE);
> +    }
> +
> +    /* at this point, xen third level pt has valid entry: means we can access
> +     * vlp2m_pte vlp2m_pte is like a fourth level pt for xen, but for guest,
> +     * it is third level pt */
> +    if ( vlp2m_pte->p2m.valid && vlp2m_pte->p2m.write == 0 )
> +    {
> +        vlp2m_pte->p2m.write = 1;
> +        vlp2m_pte->p2m.avail = 1;
> +        write_pte(vlp2m_pte, *vlp2m_pte);
> +        flush_tlb_local();
> +    }
> +
> +out:
> +    spin_unlock(&p2m->lock);
> +    return rc;
> +}
> +
>  /*
>   * Local variables:
>   * mode: C
> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> index 1b9209d..f844f56 100644
> --- a/xen/arch/arm/traps.c
> +++ b/xen/arch/arm/traps.c
> @@ -1226,7 +1226,12 @@ static void do_trap_data_abort_guest(struct 
> cpu_user_regs *regs,
>          goto bad_data_abort;
>  
>      /* XXX: Decode the instruction if ISS is not valid */
> -    if ( !dabt.valid )
> +    /* Note: add additional check before goto bad_data_abort. dabt.valid 
> +     * bit is for telling the validity of ISS[23:16] bits. For dirty-page 
> +     * tracing, we need to see DFSC bits. If DFSC bits are indicating the 
> +     * possibility of dirty page tracing, do not go to bad_data_abort */
> +    if ( !dabt.valid &&
> +         (dabt.dfsc & FSC_MASK) != (FSC_FLT_PERM + FSC_3D_LEVEL) && 
> dabt.write)
>          goto bad_data_abort;
>  
>      if (handle_mmio(&info))
> @@ -1235,6 +1240,15 @@ static void do_trap_data_abort_guest(struct 
> cpu_user_regs *regs,
>          return;
>      }
>  
> +    /* handle permission fault on write */
> +    if ( (dabt.dfsc & FSC_MASK) == (FSC_FLT_PERM + FSC_3D_LEVEL) && 
> dabt.write )
> +    {
> +        if ( current->domain->arch.dirty.mode == 0 )
> +           goto bad_data_abort;
> +        if ( handle_page_fault(current->domain, info.gpa) == 0 )
> +            return;
> +    }
> +
>  bad_data_abort:
>  
>      msg = decode_fsc( dabt.dfsc, &level);
> diff --git a/xen/include/asm-arm/domain.h b/xen/include/asm-arm/domain.h
> index 0c80c65..413b89a 100644
> --- a/xen/include/asm-arm/domain.h
> +++ b/xen/include/asm-arm/domain.h
> @@ -110,6 +110,17 @@ struct arch_domain
>          spinlock_t             lock;
>      } uart0;
>  
> +    /* dirty-page tracing */
> +    struct {
> +        spinlock_t lock;
> +        int mode;
> +        unsigned int count;
> +        uint32_t gmfn_guest_start;  /* guest physical memory start address */
> +        void *vlpt_start;           /* va-start of guest p2m */
> +        void *vlpt_end;             /* va-end of guest p2m */
> +        struct page_info *head;     /* maintain the mapped vaddrs */
> +    } dirty;
> +
>      struct dt_mem_info map_domain;
>      spinlock_t         map_lock;
>  }  __cacheline_aligned;
> diff --git a/xen/include/asm-arm/mm.h b/xen/include/asm-arm/mm.h
> index 404ec4d..fd976e3 100644
> --- a/xen/include/asm-arm/mm.h
> +++ b/xen/include/asm-arm/mm.h
> @@ -328,6 +328,11 @@ static inline void put_page_and_type(struct page_info 
> *page)
>      put_page(page);
>  }
>  
> +enum mg { mg_clear, mg_ro, mg_rw, mg_rx };
> +
> +/* routine for dirty-page tracing */
> +int handle_page_fault(struct domain *d, paddr_t addr);
> +
>  #endif /*  __ARCH_ARM_MM__ */
>  /*
>   * Local variables:
> diff --git a/xen/include/asm-arm/processor.h b/xen/include/asm-arm/processor.h
> index 06b0b25..34c21de 100644
> --- a/xen/include/asm-arm/processor.h
> +++ b/xen/include/asm-arm/processor.h
> @@ -383,6 +383,8 @@ union hsr {
>  #define FSC_CPR        (0x3a) /* Coprocossor Abort */
>  
>  #define FSC_LL_MASK    (0x03<<0)
> +#define FSC_MASK       (0x3f) /* Fault status mask */
> +#define FSC_3D_LEVEL   (0x03) /* Third level fault*/
>  
>  /* Time counter hypervisor control register */
>  #define CNTHCTL_PA      (1u<<0)  /* Kernel/user access to physical counter */
> -- 
> 1.8.1.2
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxx
> http://lists.xen.org/xen-devel
> 

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