Re: [Xen-ia64-devel] [PATCH][RFC]copy_from/to_guest

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

Hi.

Sorry for delayed point out.
At first I thought your hack would be replaced with xencomm.
However it seems to take a while to merge xencomm for IA64 so that
I decided to point it out now.


On Fri, Aug 11, 2006 at 07:01:10PM +0900, Kouya SHIMURA wrote:
Content-Description: message body text
> diff -r fc6c3d866477 xen/arch/ia64/xen/vcpu.c
> --- a/xen/arch/ia64/xen/vcpu.c        Wed Aug 09 10:32:23 2006 -0600
> +++ b/xen/arch/ia64/xen/vcpu.c        Fri Aug 11 18:35:31 2006 +0900
> @@ -2215,3 +2215,27 @@ IA64FAULT vcpu_ptr_i(VCPU *vcpu,UINT64 v
>  
>       return IA64_NO_FAULT;
>  }
> +
> +int ia64_map_hypercall_param(void)
> +{
> +     struct vcpu *v = current;
> +     struct domain *d = current->domain;
> +     u64 vaddr = v->arch.hypercall_param.va & PAGE_MASK;
> +     volatile pte_t* pte;
> +
> +     if (v->arch.hypercall_param.va == 0)
> +             return FALSE;
> +     pte = lookup_noalloc_domain_pte(d, v->arch.hypercall_param.pa1);
> +     if (!pte || !pte_present(*pte))
> +             return FALSE;
> +     vcpu_itc_no_srlz(v, 2, vaddr, pte_val(*pte), -1UL, PAGE_SHIFT);
> +     if (v->arch.hypercall_param.pa2) {
> +             vaddr += PAGE_SIZE;
> +             pte = lookup_noalloc_domain_pte(d, v->arch.hypercall_param.pa2);
> +             if (pte && pte_present(*pte)) {
> +                     vcpu_itc_no_srlz(v, 2, vaddr, pte_val(*pte), -1UL, 
> PAGE_SHIFT);
> +             }
> +     }
> +     ia64_srlz_d();
> +     return TRUE;
> +}


This isn't SMP-safe. Since the p2m table is locklesss,
another vcpu might change the p2m table entry after checking pte_present()
but before vcpu_itc_no_srlz(). You must be aware of it.

-- 
yamahata

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