On Thu, Nov 11, 2010 at 06:38:47PM +0000, Prasad Joshi wrote:
> Hello All,
>
> I have question on code of rmap_add
>
> Here is the code of the function
>
> 613 static int rmap_add(struct kvm_vcpu *vcpu, u64 *spte, gfn_t gfn)
> 614 {
>
> 624 rmapp = gfn_to_rmap(vcpu->kvm, gfn, sp->role.level);
> 625 if (!*rmapp) {
> 626 rmap_printk("rmap_add: %p %llx 0->1\n", spte, *spte);
> 627 *rmapp = (unsigned long)spte;
> 628 } else if (!(*rmapp & 1)) {
> 629 rmap_printk("rmap_add: %p %llx 1->many\n", spte, *spte);
> 630 desc = mmu_alloc_rmap_desc(vcpu);
> 631 desc->sptes[0] = (u64 *)*rmapp;
> 632 desc->sptes[1] = spte;
> 633 *rmapp = (unsigned long)desc | 1;
> 634 ++count;
> 635 } else {
>
> The line 628 checks whether the last bit of the rmapp is 1.
> If it is one then line 633 assigns a new value to rmapp with and sets
> the last bit to 1.
No, line 628 checks if the last bit is not 1, so the check works.
Joerg
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