Re: [PATCH v10 03/14] KVM: X86: Don't track dirty for KVM_SET_[TSS_ADDR|IDENTITY_MAP_ADDR]

Peter Xu
2020-07-03T19:02:59Z

On Thu, Jul 02, 2020 at 05:05:57PM -0700, Sean Christopherson wrote:
> > /* Set up identity-mapping pagetable for EPT in real mode */
> > for (i = 0; i < PT32_ENT_PER_PAGE; i++) {
> > tmp = (i << 22) + (_PAGE_PRESENT | _PAGE_RW | _PAGE_USER |
> > _PAGE_ACCESSED | _PAGE_DIRTY | _PAGE_PSE);
> > - r = kvm_write_guest_page(kvm, identity_map_pfn,
> > - &tmp, i * sizeof(tmp), sizeof(tmp));
> > - if (r < 0)
> > + r = __copy_to_user(uaddr + i * sizeof(tmp), &tmp, sizeof(tmp));
> > + if (r) {
> > + r = -EFAULT;
>
> Another case where capturing the result is unnecessary. I don't have a
> preference as to whether the result of __copy_{to,from}_user() is returned
> directly or morphed to -EFAULT, but we should be consistent, especially
> within a single patch.

OK, I'll clean all these __copy_to_user() callers in the next version.

>
> > goto out;
> > + }
> > }
> > kvm_vmx->ept_identity_pagetable_done = true;
> >
> > @@ -3532,19 +3525,22 @@ static void seg_setup(int seg)
> > static int alloc_apic_access_page(struct kvm *kvm)
> > {
> > struct page *page;
> > - int r = 0;
> > + void __user *r;
> > + int ret = 0;
> >
> > mutex_lock(&kvm->slots_lock);
> > if (kvm->arch.apic_access_page_done)
> > goto out;
> > r = __x86_set_memory_region(kvm, APIC_ACCESS_PAGE_PRIVATE_MEMSLOT,
> > APIC_DEFAULT_PHYS_BASE, PAGE_SIZE);
>
> Naming the new 'void __user *hva' would yield a smaller differ and would
> probably help readers in the future.

OK.

> > } else {
> > - if (!slot || !slot->npages)
> > - return 0;
> > -
> > /*
> > * Stuff a non-canonical value to catch use-after-delete. This
> > * ends up being 0 on 32-bit KVM, but there's no better
> > * alternative.
> > */
> > hva = (unsigned long)(0xdeadull << 48);
> > +
> > + if (!slot || !slot->npages)
> > + return (void __user *)hva;
>
> My clever shenanigans got discarded, so this weirdness happily is gone.

I'll see what I get when I rebase. This series is easy to encounter conflicts
during previous rebases for misterious reasons. I guess I'll just repost less
frequently so I suffer less from rebase too. :)

Thanks.

--
Peter Xu