On 11/13/2012 07:12 AM, Marcelo Tosatti wrote: > On Mon, Nov 05, 2012 at 08:10:08PM +0800, Xiao Guangrong wrote: >> In order to detecting spte remapping, we can simply check whether the >> spte has already been pointing to the pfn even if the spte is not the >> last spte for middle spte is pointing to the kernel pfn which can not >> be mapped to userspace >> >> Also, update slot and stat.lpages iff the spte is not remapped >> >> Signed-off-by: Xiao Guangrong <[email protected]> >> --- >> arch/x86/kvm/mmu.c | 40 +++++++++++++--------------------------- >> 1 files changed, 13 insertions(+), 27 deletions(-) >> >> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c >> index 692ebb1..4ea731e 100644 >> --- a/arch/x86/kvm/mmu.c >> +++ b/arch/x86/kvm/mmu.c >> @@ -2420,8 +2420,7 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 >> *sptep, >> pfn_t pfn, bool speculative, >> bool host_writable) >> { >> - int was_rmapped = 0; >> - int rmap_count; >> + bool was_rmapped = false; >> >> pgprintk("%s: spte %llx access %x write_fault %d" >> " user_fault %d gfn %llx\n", >> @@ -2429,25 +2428,13 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 >> *sptep, >> write_fault, user_fault, gfn); >> >> if (is_rmap_spte(*sptep)) { >> - /* >> - * If we overwrite a PTE page pointer with a 2MB PMD, unlink >> - * the parent of the now unreachable PTE. >> - */ >> - if (level > PT_PAGE_TABLE_LEVEL && >> - !is_large_pte(*sptep)) { >> - struct kvm_mmu_page *child; >> - u64 pte = *sptep; >> + if (pfn != spte_to_pfn(*sptep)) { >> + struct kvm_mmu_page *sp = page_header(__pa(sptep)); >> >> - child = page_header(pte & PT64_BASE_ADDR_MASK); >> - drop_parent_pte(child, sptep); >> - kvm_flush_remote_tlbs(vcpu->kvm); > > How come its safe to drop this case?
We use "if (pfn != spte_to_pfn(*sptep))" to simplify the thing. There are two cases: 1) the sptep is not the last mapping. under this case, sptep must point to a shadow page table, that means spte_to_pfn(*sptep)) is used by KVM module, and 'pfn' is used by userspace. so, 'if' condition must be satisfied, the sptep will be dropped. Actually, This is the origin case: | if (level > PT_PAGE_TABLE_LEVEL && | !is_large_pte(*sptep))" 2) the sptep is the last mapping. under this case, the level of spte (sp.level) must equal the 'level' which we pass to mmu_set_spte. If they point to the same pfn, it is 'remap', otherwise we drop it. I think this is safe. :) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
