On Thu, Sep 26, 2019 at 10:46:38AM +0100, hong...@amazon.com wrote:
> From: Hongyan Xia <hong...@amazon.com>
>
> Signed-off-by: Hongyan Xia <hong...@amazon.com>
> ---
> xen/arch/x86/mm.c | 36 ++++++++++++++++++++++++++++++++++--
> 1 file changed, 34 insertions(+), 2 deletions(-)
>
> diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
> index ab760ecc1f..39ba9f9bf4 100644
> --- a/xen/arch/x86/mm.c
> +++ b/xen/arch/x86/mm.c
> @@ -5058,8 +5058,40 @@ l1_pgentry_t *virt_to_xen_l1e(unsigned long v)
>
> unsigned long virt_to_mfn_walk(void *va)
> {
> - l1_pgentry_t *pl1e = virt_to_xen_l1e((unsigned long)(va));
> - unsigned long ret = l1e_get_pfn(*pl1e);
> + unsigned long ret;
> + l3_pgentry_t *pl3e;
> + l2_pgentry_t *pl2e;
> + l1_pgentry_t *pl1e;
> +
> + /*
> + * FIXME: This is rather unoptimised, because e.g. virt_to_xen_l2e
> + * recomputes virt_to_xen_l3e again. Clearly one can keep the result and
> + * carry on.
> + */
> +
> + pl3e = virt_to_xen_l3e((unsigned long)(va));
> + BUG_ON(!(l3e_get_flags(*pl3e) & _PAGE_PRESENT));
> + if ( l3e_get_flags(*pl3e) & _PAGE_PSE )
> + {
> + ret = l3e_get_pfn(*pl3e);
> + ret |= (((unsigned long)va & ((1UL << L3_PAGETABLE_SHIFT)-1)) >>
> PAGE_SHIFT);
> + unmap_xen_pagetable(pl3e);
> + return ret;
> + }
> +
> + pl2e = virt_to_xen_l2e((unsigned long)(va));
> + BUG_ON(!(l2e_get_flags(*pl2e) & _PAGE_PRESENT));
> + if ( l2e_get_flags(*pl2e) & _PAGE_PSE )
> + {
> + ret = l2e_get_pfn(*pl2e);
> + ret |= (((unsigned long)va & ((1UL << L2_PAGETABLE_SHIFT)-1)) >>
> PAGE_SHIFT);
> + unmap_xen_pagetable(pl2e);
> + return ret;
> + }
> +
> + pl1e = virt_to_xen_l1e((unsigned long)(va));
> + BUG_ON(!(l1e_get_flags(*pl1e) & _PAGE_PRESENT));
> + ret = l1e_get_pfn(*pl1e);
Don't you end up leaking pl3e and pl2e in the !PSE case?
Also, if you only want to walk page table that is already populated,
there may be a better way to do it than calling virt_to_xen_lXe.
Wei.
> unmap_xen_pagetable(pl1e);
> return ret;
> }
> --
> 2.17.1
>
>
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