Re: [Xen-devel] [PATCH 16/20] xen/arm: mm: Protect Xen page-table update with a spinlock

[Andrii Anisov <andrii.anisov@xxxxxxxxx>]

Hello Julien,

On 22.04.19 19:49, Julien Grall wrote:
> The function create_xen_entries may be concurrently called. So we need
> to protect with a spinlock to avoid corruption the page-tables.
The question from me is why didn't we step into this issue before?

> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> ---
>   xen/arch/arm/mm.c | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index fa0f41bd07..ecde4e34df 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -969,6 +969,8 @@ enum xenmap_operation {
>       RESERVE
>   };
>   
> +static DEFINE_SPINLOCK(xen_pt_lock);
> +
>   static int create_xen_entries(enum xenmap_operation op,
>                                 unsigned long virt,
>                                 mfn_t mfn,
> @@ -980,6 +982,8 @@ static int create_xen_entries(enum xenmap_operation op,
>       lpae_t pte, *entry;
>       lpae_t *third = NULL;
>   
> +    spin_lock(&xen_pt_lock);
> +
>       for(; addr < addr_end; addr += PAGE_SIZE, mfn = mfn_add(mfn, 1))
>       {
>           entry = &xen_second[second_linear_offset(addr)];
> @@ -1054,6 +1058,8 @@ out:
>        */
>       flush_xen_tlb_range_va(virt, PAGE_SIZE * nr_mfns);
>   
> +    spin_unlock(&xen_pt_lock);
> +
>       return rc;
>   }
>   

--
Sincerely,
Andrii Anisov.

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