Re: [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 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
Cc: "Radim Krčmář"
Cc: Sean Christopherson
Cc: Vitaly Kuznetsov
Cc: Wanpeng Li
Cc: Jim Mattson
Cc: Joerg Roedel
Cc: Thomas Gleixner
Cc: Ingo Molnar
Cc: Borislav Petkov
Cc: "H. Peter Anvin"
Cc: KarimAllah Ahmed
Cc: Michal Hocko
Cc: Dan Williams
Signed-off-by: David Hildenbrand
---
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
--
Thanks,
David / dhildenb
Re: [PATCH v1 02/10] KVM: x86/mmu: Prepare kvm_is_mmio_pfn() for PG_reserved changes
On Thu, Oct 24, 2019 at 5:10 AM David Hildenbrand 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
> Cc: "Radim Krčmář"
> Cc: Sean Christopherson
> Cc: Vitaly Kuznetsov
> Cc: Wanpeng Li
> Cc: Jim Mattson
> Cc: Joerg Roedel
> Cc: Thomas Gleixner
> Cc: Ingo Molnar
> Cc: Borislav Petkov
> Cc: "H. Peter Anvin"
> Cc: KarimAllah Ahmed
> Cc: Michal Hocko
> Cc: Dan Williams
> Signed-off-by: David Hildenbrand
> ---
> 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
[PATCH v1 02/10] KVM: x86/mmu: Prepare kvm_is_mmio_pfn() for PG_reserved changes
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
Cc: "Radim Krčmář"
Cc: Sean Christopherson
Cc: Vitaly Kuznetsov
Cc: Wanpeng Li
Cc: Jim Mattson
Cc: Joerg Roedel
Cc: Thomas Gleixner
Cc: Ingo Molnar
Cc: Borislav Petkov
Cc: "H. Peter Anvin"
Cc: KarimAllah Ahmed
Cc: Michal Hocko
Cc: Dan Williams
Signed-off-by: David Hildenbrand
---
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.
+*/
if (pfn_valid(pfn))
- return !is_zero_pfn(pfn) && PageReserved(pfn_to_page(pfn)) &&
- /*
-* Some reserved pages, such as those from NVDIMM
-* DAX devices, are not for MMIO, and can be mapped
-* with cached memory type for better performance.
-* However, the above check misconceives those pages
-* as MMIO, and results in KVM mapping them with UC
-* memory type, which would hurt the performance.
-* Therefore, we check the host memory type in addition
-* and only treat UC/UC-/WC pages as MMIO.
-*/
- (!pat_enabled() || pat_pfn_immune_to_uc_mtrr(pfn));
+ return !pat_enabled() || pat_pfn_immune_to_uc_mtrr(pfn);
+ /*
+* Any RAM that has no memmap (e.g., mapped via /dev/mem) is not MMIO.
+*/
return !e820__mapped_raw_any(pfn_to_hpa(pfn),
pfn_to_hpa(pfn + 1) - 1,
E820_TYPE_RAM);
--
2.21.0
