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



On 05.11.19 02:37, Dan Williams wrote:
On Thu, Oct 24, 2019 at 5:10 AM David Hildenbrand <david@xxxxxxxxxx> 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@xxxxxxxxxx>
Cc: "Radim Krčmář" <rkrcmar@xxxxxxxxxx>
Cc: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Cc: Wanpeng Li <wanpengli@xxxxxxxxxxx>
Cc: Jim Mattson <jmattson@xxxxxxxxxx>
Cc: Joerg Roedel <joro@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: KarimAllah Ahmed <karahmed@xxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
  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().

/*
 * Anything with a valid (but not online) memmap could be ZONE_DEVICE.
 * Treat only UC/UC-/WC pages as MMIO. devm_memremap_pages() established
 * the correct memtype for WB cacheable ZONE_DEVICE pages.
 */

Thanks!


Other than that, feel free to add:

Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>



--

Thanks,

David / dhildenb


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