On 17/02/2018 19:01, 丁卓成 wrote:
> In `set_spte`, where we prepare a new spte entry, we have this:
>> if (pte_access & ACC_WRITE_MASK) {
>> kvm_vcpu_mark_page_dirty(vcpu, gfn);
>> spte |= spte_shadow_dirty_mask(spte);
>> }
> And in `__direct_map`, we have this:
>> emulate = mmu_set_spte(vcpu, iterator.sptep, ACC_ALL,
>> write, level, gfn, pfn, prefault,
>> map_writable);
> If Guest issue a read to a page, and the corresponding spte is not present,
> `__direct_map` will be called to build the spte (and maybe parent sps as well)
> in EPT mode and SPT nonpaging mode. Since we pass ACC_ALL to `set_spte` in this
> case, even a read fault will cause the page to be marked dirty in dirty bitmap,
> and it will also set the D bit in spte.
Hi, the "ACC_ALL" is fixed here in set_spte:
if (host_writable)
spte |= SPTE_HOST_WRITEABLE;
else
pte_access &= ~ACC_WRITE_MASK;
where host_writable is the last argument to mmu_set_spte.
Thanks,
Paolo
