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SubjectRe: [PATCH v3 2/9] KVM: MMU: abstract spte write-protect
On 04/21/2012 12:18 PM, Marcelo Tosatti wrote:

> On Sat, Apr 21, 2012 at 11:24:54AM +0800, Xiao Guangrong wrote:
>> On 04/21/2012 05:33 AM, Marcelo Tosatti wrote:
>>
>>
>>>> static bool
>>>> __rmap_write_protect(struct kvm *kvm, unsigned long *rmapp, int level)
>>>> {
>>>> @@ -1050,24 +1078,13 @@ __rmap_write_protect(struct kvm *kvm, unsigned long *rmapp, int level)
>>>>
>>>> for (sptep = rmap_get_first(*rmapp, &iter); sptep;) {
>>>> BUG_ON(!(*sptep & PT_PRESENT_MASK));
>>>> - rmap_printk("rmap_write_protect: spte %p %llx\n", sptep, *sptep);
>>>> -
>>>> - if (!is_writable_pte(*sptep)) {
>>>> - sptep = rmap_get_next(&iter);
>>>> - continue;
>>>> - }
>>>> -
>>>> - if (level == PT_PAGE_TABLE_LEVEL) {
>>>> - mmu_spte_update(sptep, *sptep & ~PT_WRITABLE_MASK);
>>>> - sptep = rmap_get_next(&iter);
>>>> - } else {
>>>> - BUG_ON(!is_large_pte(*sptep));
>>>> - drop_spte(kvm, sptep);
>>>> - --kvm->stat.lpages;
>>>
>>> It is preferable to remove all large sptes including read-only ones, the
>>
>>
>> It can cause page faults even if read memory on these large sptse.
>>
>> Actually, Avi suggested that make large writable spte to be readonly
>> (not dropped) on this path.
>
> See commits e49146dce8c3dc6f4485c1904b6587855f393e71,
> 38187c830cab84daecb41169948467f1f19317e3 for issues
> with large read-only sptes.
>


Yes, we need check the code carefully when change writable spte to be
read-only, let us discuss it in the separate patchset later. :)



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