Hi, I'm learning kvm-mmu codes, when I was reading codes from this patch,
I can't understand why we need to do special process for "writable pte".
> +static int kvm_set_pte_rmapp(struct kvm *kvm, unsigned long *rmapp,
> + unsigned long data)
> +{
> + int need_flush = 0;
> + u64 *spte, new_spte;
> + pte_t *ptep = (pte_t *)data;
> + pfn_t new_pfn;
> +
> + new_pfn = pte_pfn(ptep_val(ptep));
> + spte = rmap_next(kvm, rmapp, NULL);
> + while (spte) {
> + BUG_ON(!is_shadow_present_pte(*spte));
> + rmap_printk("kvm_set_pte_rmapp: spte %p %llx\n", spte, *spte);
> + need_flush = 1;
> + if (pte_write(ptep_val(ptep))) {
> + rmap_remove(kvm, spte);
> + set_shadow_pte(spte, shadow_trap_nonpresent_pte);
> + spte = rmap_next(kvm, rmapp, NULL);
> + } else {
> + new_spte = *spte &~ (PT64_BASE_ADDR_MASK);
> + new_spte |= new_pfn << PAGE_SHIFT;
> +
> + if (!pte_write(ptep_val(ptep))) {
> + new_spte &= ~PT_WRITABLE_MASK;
> + new_spte &= ~SPTE_HOST_WRITEABLE;
> + if (is_writeble_pte(*spte))
> + kvm_set_pfn_dirty(spte_to_pfn(*spte));
> + }
> + set_shadow_pte(spte, new_spte);
> + spte = rmap_next(kvm, rmapp, spte);
> + }
> + }
> + if (need_flush)
> + kvm_flush_remote_tlbs(kvm);
> +
> + return 0;
> +}
> +
In my opinion, we can just regard writable pte same as readable/executable,
all the corresponding sptes will be set as write-protect, and when guest
access them, an EPT-violation occurs and we do this #PF in kvm.
Shall anyone has some hint ?
On 2009/3/31 08:00, Izik Eidus wrote:
apply it against Avi git tree.
Izik Eidus (3):
kvm: dont hold pagecount reference for mapped sptes pages.
kvm: add SPTE_HOST_WRITEABLE flag to the shadow ptes.
kvm: add support for change_pte mmu notifiers
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/mmu.c | 89 ++++++++++++++++++++++++++++++++-------
arch/x86/kvm/paging_tmpl.h | 16 ++++++-
virt/kvm/kvm_main.c | 14 ++++++
4 files changed, 101 insertions(+), 19 deletions(-)
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
