[PATCH v4 0/6] Update document description for kvm_mmu_page and kvm_mmu_page_role

[PATCH v4 0/6] Update document description for kvm_mmu_page and kvm_mmu_page_role

[Mingwei Zhang]

This is 4th version of the series, minor fixes as follows:
 - correct the descripotion of tdp_mmu_root_count [seanjc]
 - update the descripotion of mmu_valid_gen [seanjc]

v3: https://lore.kernel.org/all/20230801002127.534020-1-mizhang@google.com/

Mingwei Zhang (6):
  KVM: Documentation: Add the missing description for guest_mode in
    kvm_mmu_page_role
  KVM: Documentation: Update the field name gfns and its description in
    kvm_mmu_page
  KVM: Documentation: Add the missing description for ptep in
    kvm_mmu_page
  KVM: Documentation: Add the missing description for tdp_mmu_root_count
    into kvm_mmu_page
  KVM: Documentation: Add the missing description for mmu_valid_gen into
    kvm_mmu_page
  KVM: Documentation: Add the missing description for tdp_mmu_page into
    kvm_mmu_page

 Documentation/virt/kvm/x86/mmu.rst | 43 +++++++++++++++++++++++-------
 1 file changed, 34 insertions(+), 9 deletions(-)


base-commit: bfd926291c585600ace63ea3b6eb1458aa067f4f
-- 
2.42.0.283.g2d96d420d3-goog

[PATCH v4 1/6] KVM: Documentation: Add the missing description for guest_mode in kvm_mmu_page_role

[Mingwei Zhang]

Add the missing description for guest_mode in kvm_mmu_page_role
description.  guest_mode tells KVM whether a shadow page is used for the L1
or an L2. Update the missing field in documentation.

Signed-off-by: Mingwei Zhang <mizhang@google.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
---
 Documentation/virt/kvm/x86/mmu.rst | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Documentation/virt/kvm/x86/mmu.rst b/Documentation/virt/kvm/x86/mmu.rst
index 26f62034b6f3..23c20455d4e7 100644
--- a/Documentation/virt/kvm/x86/mmu.rst
+++ b/Documentation/virt/kvm/x86/mmu.rst
@@ -202,6 +202,8 @@ Shadow pages contain the following information:
     Is 1 if the MMU instance cannot use A/D bits.  EPT did not have A/D
     bits before Haswell; shadow EPT page tables also cannot use A/D bits
     if the L1 hypervisor does not enable them.
+  role.guest_mode:
+    Indicates the shadow page is created for a nested guest.
   role.passthrough:
     The page is not backed by a guest page table, but its first entry
     points to one.  This is set if NPT uses 5-level page tables (host
-- 
2.42.0.283.g2d96d420d3-goog

[PATCH v4 2/6] KVM: Documentation: Update the field name gfns and its description in kvm_mmu_page

[Mingwei Zhang]

Update the field 'gfns' in kvm_mmu_page to 'shadowed_translation' to be
consistent with the code. Also update the corresponding 'gfns' in the
comments. The more detailed description of 'shadowed_translation' is
already inlined in the data structure definition, so no need to duplicate
the text but simply just update the names.

Signed-off-by: Mingwei Zhang <mizhang@google.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
---
 Documentation/virt/kvm/x86/mmu.rst | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/Documentation/virt/kvm/x86/mmu.rst b/Documentation/virt/kvm/x86/mmu.rst
index 23c20455d4e7..f659f282357d 100644
--- a/Documentation/virt/kvm/x86/mmu.rst
+++ b/Documentation/virt/kvm/x86/mmu.rst
@@ -221,11 +221,14 @@ Shadow pages contain the following information:
     at __pa(sp2->spt).  sp2 will point back at sp1 through parent_pte.
     The spt array forms a DAG structure with the shadow page as a node, and
     guest pages as leaves.
-  gfns:
-    An array of 512 guest frame numbers, one for each present pte.  Used to
-    perform a reverse map from a pte to a gfn. When role.direct is set, any
-    element of this array can be calculated from the gfn field when used, in
-    this case, the array of gfns is not allocated. See role.direct and gfn.
+  shadowed_translation:
+    An array of 512 shadow translation entries, one for each present pte. Used
+    to perform a reverse map from a pte to a gfn as well as its access
+    permission. When role.direct is set, the shadow_translation array is not
+    allocated. This is because the gfn contained in any element of this array
+    can be calculated from the gfn field when used.  In addition, when
+    role.direct is set, KVM does not track access permission for each of the
+    gfn. See role.direct and gfn.
   root_count:
     A counter keeping track of how many hardware registers (guest cr3 or
     pdptrs) are now pointing at the page.  While this counter is nonzero, the
-- 
2.42.0.283.g2d96d420d3-goog

[PATCH v4 3/6] KVM: Documentation: Add the missing description for ptep in kvm_mmu_page

[Mingwei Zhang]

Add the missing description for ptep in kvm_mmu_page description. ptep is
used when TDP MMU is enabled and it shares the storage with parent_ptes.
Update the doc to help readers to get up-to-date info.

Signed-off-by: Mingwei Zhang <mizhang@google.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
---
 Documentation/virt/kvm/x86/mmu.rst | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Documentation/virt/kvm/x86/mmu.rst b/Documentation/virt/kvm/x86/mmu.rst
index f659f282357d..22d221c180d7 100644
--- a/Documentation/virt/kvm/x86/mmu.rst
+++ b/Documentation/virt/kvm/x86/mmu.rst
@@ -239,6 +239,9 @@ Shadow pages contain the following information:
     parent_ptes points at this single spte, otherwise, there exists multiple
     sptes pointing at this page and (parent_ptes & ~0x1) points at a data
     structure with a list of parent sptes.
+  ptep:
+    The kernel virtual address of the SPTE that points at this shadow page.
+    Used exclusively by the TDP MMU, this field is a union with parent_ptes.
   unsync:
     If true, then the translations in this page may not match the guest's
     translation.  This is equivalent to the state of the tlb when a pte is
-- 
2.42.0.283.g2d96d420d3-goog

[PATCH v4 4/6] KVM: Documentation: Add the missing description for tdp_mmu_root_count into kvm_mmu_page

[Mingwei Zhang]

Add the description of tdp_mmu_root_count into kvm_mmu_page description and
combine it with the description of root_count. tdp_mmu_root_count is an
atomic counter used only in TDP MMU. Update the doc.

Signed-off-by: Mingwei Zhang <mizhang@google.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
---
 Documentation/virt/kvm/x86/mmu.rst | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/Documentation/virt/kvm/x86/mmu.rst b/Documentation/virt/kvm/x86/mmu.rst
index 22d221c180d7..4a82fa016833 100644
--- a/Documentation/virt/kvm/x86/mmu.rst
+++ b/Documentation/virt/kvm/x86/mmu.rst
@@ -229,10 +229,13 @@ Shadow pages contain the following information:
     can be calculated from the gfn field when used.  In addition, when
     role.direct is set, KVM does not track access permission for each of the
     gfn. See role.direct and gfn.
-  root_count:
-    A counter keeping track of how many hardware registers (guest cr3 or
-    pdptrs) are now pointing at the page.  While this counter is nonzero, the
-    page cannot be destroyed.  See role.invalid.
+  root_count / tdp_mmu_root_count:
+     root_count is a reference counter for root shadow pages in Shadow MMU.
+     vCPUs elevate the refcount when getting a shadow page that will be used as
+     a root page, i.e. page that will be loaded into hardware directly (CR3,
+     PDPTRs, nCR3 EPTP). Root pages cannot be destroyed while their refcount is
+     non-zero. See role.invalid. tdp_mmu_root_count is similar but exclusively
+     used in TDP MMU as an atomic refcount.
   parent_ptes:
     The reverse mapping for the pte/ptes pointing at this page's spt. If
     parent_ptes bit 0 is zero, only one spte points at this page and
-- 
2.42.0.283.g2d96d420d3-goog

[PATCH v4 5/6] KVM: Documentation: Add the missing description for mmu_valid_gen into kvm_mmu_page

[Mingwei Zhang]

Add the description for mmu_valid_gen into kvm_mmu_page description.
mmu_valid_gen is used in shadow MMU for fast zapping. Update the doc to
reflect that.

Signed-off-by: Mingwei Zhang <mizhang@google.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
---
 Documentation/virt/kvm/x86/mmu.rst | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/Documentation/virt/kvm/x86/mmu.rst b/Documentation/virt/kvm/x86/mmu.rst
index 4a82fa016833..16d5d6a1c174 100644
--- a/Documentation/virt/kvm/x86/mmu.rst
+++ b/Documentation/virt/kvm/x86/mmu.rst
@@ -208,6 +208,16 @@ Shadow pages contain the following information:
     The page is not backed by a guest page table, but its first entry
     points to one.  This is set if NPT uses 5-level page tables (host
     CR4.LA57=1) and is shadowing L1's 4-level NPT (L1 CR4.LA57=0).
+  mmu_valid_gen:
+    The MMU generation of this page, used to fast zap of all MMU pages within a
+    VM without blocking vCPUs too long. Specifically, KVM updates the per-VM
+    valid MMU generation which causes the mismatch of mmu_valid_gen for each mmu
+    page. This makes all existing MMU pages obsolete. Obsolete pages can't be
+    used. Therefore, vCPUs must load a new, valid root before re-entering the
+    guest. The MMU generation is only ever '0' or '1'. Note, the TDP MMU doesn't
+    use this field as non-root TDP MMU pages are reachable only from their
+    owning root. Thus it suffices for TDP MMU to use role.invalid in root pages
+    to invalidate all MMU pages.
   gfn:
     Either the guest page table containing the translations shadowed by this
     page, or the base page frame for linear translations.  See role.direct.
-- 
2.42.0.283.g2d96d420d3-goog

[PATCH v4 6/6] KVM: Documentation: Add the missing description for tdp_mmu_page into kvm_mmu_page

[Mingwei Zhang]

Add the description for tdp_mmu_page into kvm_mmu_page description.
tdp_mmu_page is a field to differentiate shadow pages from TDP MMU and
non-TDP MMU.

Signed-off-by: Mingwei Zhang <mizhang@google.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
---
 Documentation/virt/kvm/x86/mmu.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Documentation/virt/kvm/x86/mmu.rst b/Documentation/virt/kvm/x86/mmu.rst
index 16d5d6a1c174..82c5c6a6da2c 100644
--- a/Documentation/virt/kvm/x86/mmu.rst
+++ b/Documentation/virt/kvm/x86/mmu.rst
@@ -282,6 +282,10 @@ Shadow pages contain the following information:
     since the last time the page table was actually used; if emulation
     is triggered too frequently on this page, KVM will unmap the page
     to avoid emulation in the future.
+  tdp_mmu_page:
+    Is 1 if the shadow page is a TDP MMU page. This variable is used to
+    bifurcate the control flows for KVM when walking any data structure that may
+    contain pages from both TDP MMU and shadow MMU.
 
 Reverse map
 ===========
-- 
2.42.0.283.g2d96d420d3-goog

Re: [PATCH v4 0/6] Update document description for kvm_mmu_page and kvm_mmu_page_role

[Sean Christopherson]

On Tue, 12 Sep 2023 18:45:47 +0000, Mingwei Zhang wrote:
> This is 4th version of the series, minor fixes as follows:
>  - correct the descripotion of tdp_mmu_root_count [seanjc]
>  - update the descripotion of mmu_valid_gen [seanjc]
> 
> v3: https://lore.kernel.org/all/20230801002127.534020-1-mizhang@google.com/
> 
> Mingwei Zhang (6):
>   KVM: Documentation: Add the missing description for guest_mode in
>     kvm_mmu_page_role
>   KVM: Documentation: Update the field name gfns and its description in
>     kvm_mmu_page
>   KVM: Documentation: Add the missing description for ptep in
>     kvm_mmu_page
>   KVM: Documentation: Add the missing description for tdp_mmu_root_count
>     into kvm_mmu_page
>   KVM: Documentation: Add the missing description for mmu_valid_gen into
>     kvm_mmu_page
>   KVM: Documentation: Add the missing description for tdp_mmu_page into
>     kvm_mmu_page
> 
> [...]

Applied to kvm-x86 docs, thanks!

[1/6] KVM: Documentation: Add the missing description for guest_mode in kvm_mmu_page_role
      https://github.com/kvm-x86/linux/commit/b207cfbc8c1d
[2/6] KVM: Documentation: Update the field name gfns and its description in kvm_mmu_page
      https://github.com/kvm-x86/linux/commit/fdaca560b6c4
[3/6] KVM: Documentation: Add the missing description for ptep in kvm_mmu_page
      https://github.com/kvm-x86/linux/commit/b40a2455e9eb
[4/6] KVM: Documentation: Add the missing description for tdp_mmu_root_count into kvm_mmu_page
      https://github.com/kvm-x86/linux/commit/6a713928ae1c
[5/6] KVM: Documentation: Add the missing description for mmu_valid_gen into kvm_mmu_page
      https://github.com/kvm-x86/linux/commit/c3204c406b6d
[6/6] KVM: Documentation: Add the missing description for tdp_mmu_page into kvm_mmu_page
      https://github.com/kvm-x86/linux/commit/78b5605d44e6

--
https://github.com/kvm-x86/linux/tree/next