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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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