>>> + */
>>> +static int map_p2m_list(struct xc_sr_context *ctx, uint64_t p2m_cr3)
>>> +{
>>> + xc_interface *xch = ctx->xch;
>>> + xen_vaddr_t p2m_vaddr, p2m_end, mask, off;
>>> + xen_pfn_t p2m_mfn, mfn, saved_mfn, max_pfn;
>>> + uint64_t *ptes;
>>> + xen_pfn_t *mfns;
>>> + unsigned fpp, n_pages, level, shift, idx_start, idx_end, idx,
>>> saved_idx;
>>> + int rc = -1;
>>> +
>>> + p2m_mfn = cr3_to_mfn(ctx, p2m_cr3);
>>> + if ( p2m_mfn == 0 || p2m_mfn > ctx->x86_pv.max_mfn )
>> mfn 0 isn't invalid to use here. It could, in principle, be available
>> for PV guest use.
> No, the value 0 indicates that the linear p2m info isn't valid. See
> comments in xen/include/public/arch-x86/xen.h
Technically speaking, that is p2m_cr3, rather than p2m_mfn but I suppose
there is a linear mapping between the two.
As this function only gets called with a non-zero p2m_cr3, an
alternative would be assert(p2m_cr3 > 0).
The mfn == 0 comment also applies for reading the ptes in the loop below.
>
>> I believe this allows you drop 'mask' in its entirety.
> Hmm, no. I'd still have to mask possible top 16 '1' bits away.
So you would. My mistake.
~Andrew
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