[PATCH v1 02/10] KVM: x86/mmu: Prepare kvm_is_mmio_pfn() for PG_reserved changes

[Dan Williams]

On Thu, Oct 24, 2019 at 5:10 AM David Hildenbrand <david at redhat.com> wrote:
>
> Right now, ZONE_DEVICE memory is always set PG_reserved. We want to
> change that.
>
> KVM has this weird use case that you can map anything from /dev/mem
> into the guest. pfn_valid() is not a reliable check whether the memmap
> was initialized and can be touched. pfn_to_online_page() makes sure
> that we have an initialized memmap (and don't have ZONE_DEVICE memory).
>
> Rewrite kvm_is_mmio_pfn() to make sure the function produces the
> same result once we stop setting ZONE_DEVICE pages PG_reserved.
>
> Cc: Paolo Bonzini <pbonzini at redhat.com>
> Cc: "Radim Krčmář" <rkrcmar at redhat.com>
> Cc: Sean Christopherson <sean.j.christopherson at intel.com>
> Cc: Vitaly Kuznetsov <vkuznets at redhat.com>
> Cc: Wanpeng Li <wanpengli at tencent.com>
> Cc: Jim Mattson <jmattson at google.com>
> Cc: Joerg Roedel <joro at 8bytes.org>
> Cc: Thomas Gleixner <tglx at linutronix.de>
> Cc: Ingo Molnar <mingo at redhat.com>
> Cc: Borislav Petkov <bp at alien8.de>
> Cc: "H. Peter Anvin" <hpa at zytor.com>
> Cc: KarimAllah Ahmed <karahmed at amazon.de>
> Cc: Michal Hocko <mhocko at kernel.org>
> Cc: Dan Williams <dan.j.williams at intel.com>
> Signed-off-by: David Hildenbrand <david at redhat.com>
> ---
>  arch/x86/kvm/mmu.c | 29 +++++++++++++++++------------
>  1 file changed, 17 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 24c23c66b226..f03089a336de 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -2962,20 +2962,25 @@ static bool mmu_need_write_protect(struct kvm_vcpu *vcpu, gfn_t gfn,
>
>  static bool kvm_is_mmio_pfn(kvm_pfn_t pfn)
>  {
> +       struct page *page = pfn_to_online_page(pfn);
> +
> +       /*
> +        * ZONE_DEVICE pages are never online. Online pages that are reserved
> +        * either indicate the zero page or MMIO pages.
> +        */
> +       if (page)
> +               return !is_zero_pfn(pfn) && PageReserved(pfn_to_page(pfn));
> +
> +       /*
> +        * Anything with a valid (but not online) memmap could be ZONE_DEVICE.
> +        * Treat only UC/UC-/WC pages as MMIO.

You might clarify that ZONE_DEVICE pages that belong to WB cacheable
pmem have the correct memtype established by devm_memremap_pages().

Other than that, feel free to add:

Reviewed-by: Dan Williams <dan.j.williams at intel.com>