From 7b976e63a3d80c83d3944fb9dea815ad7c042195 Mon Sep 17 00:00:00 2001
From: Petr Benes <w.benny@outlook.com>
Date: Sun, 5 Jan 2020 17:05:36 +0100
Subject: [PATCH] introduce ept_t::map_identity_sparse() method

---
 src/hvpp/hvpp/ept.cpp  | 41 +++++++++++++++++++++++++++++++++++------
 src/hvpp/hvpp/ept.h    |  1 +
 src/hvpp/hvpp/hvpp.cpp | 19 +++++++++++++++++++
 src/hvpp/hvpp/hvpp.h   | 13 +++++++++++++
 4 files changed, 68 insertions(+), 6 deletions(-)

diff --git a/src/hvpp/hvpp/ept.cpp b/src/hvpp/hvpp/ept.cpp
index c017e44..19511c3 100644
--- a/src/hvpp/hvpp/ept.cpp
+++ b/src/hvpp/hvpp/ept.cpp
@@ -71,12 +71,6 @@ void ept_t::map_identity(epte_t::access_type access /* = epte_t::access_type::re
   //     loss.
   //
 
-  //
-  // TODO:
-  //   - Map only valid physical memory ranges?
-  //   - Map up to max valid physical memory address? (incl. "holes")
-  //
-
   static constexpr auto _512gb = 512ull * 1024
                                         * 1024
                                         * 1024;
@@ -87,6 +81,41 @@ void ept_t::map_identity(epte_t::access_type access /* = epte_t::access_type::re
   }
 }
 
+void ept_t::map_identity_sparse(epte_t::access_type access /* = epte_t::access_type::read_write_execute */) noexcept
+{
+  //
+  // This method is similar to the map_identity() method above, except that
+  // the memory is covered by using physical_memory_descriptor() as opposed to
+  // covering the first 512 GB of physical memory.
+  //
+  // The benefit of this approach is that it uses significantly less memory
+  // for the EPT structures. Only addresses backed by actual physical memory
+  // are mapped (considering that the machine doesn't have 512 GB+).
+  //
+  // The drawback of this approach is that it doesn't cover MMIO address ranges.
+  // Therefore there is a good chance that you'll receive several EPT violations.
+  // EPT violation handler then should create and map EPT entries for the missing
+  // pages.
+  //
+
+  //
+  // #TODO
+  // Consider combined approach where the first 4GB is mapped unconditionally (most
+  // MMIO is there) and rest is filled with physical_memory_descriptor().
+  //
+
+  for (auto& range : mm::physical_memory_descriptor())
+  {
+    auto from = pa_t{ page_align   (range.begin().value(), pd_t{}) };
+    auto to   = pa_t{ page_align_up(range.end().value(),   pd_t{}) };
+
+    for (pa_t pa = from; pa < to; pa += ept_pd_t::size)
+    {
+      map_2mb(pa, pa, access);
+    }
+  }
+}
+
 epte_t* ept_t::map(pa_t guest_pa, pa_t host_pa,
                    epte_t::access_type access /* = epte_t::access_type::read_write_execute */,
                    pml level /* = pml::pt */) noexcept
diff --git a/src/hvpp/hvpp/ept.h b/src/hvpp/hvpp/ept.h
index b661b93..c0ab660 100644
--- a/src/hvpp/hvpp/ept.h
+++ b/src/hvpp/hvpp/ept.h
@@ -20,6 +20,7 @@ class ept_t final
     ept_t& operator=(ept_t&& other) noexcept = delete;
 
     void map_identity(epte_t::access_type access = epte_t::access_type::read_write_execute) noexcept;
+    void map_identity_sparse(epte_t::access_type access = epte_t::access_type::read_write_execute) noexcept;
 
     epte_t* map    (pa_t guest_pa, pa_t host_pa,
                     epte_t::access_type access = epte_t::access_type::read_write_execute,
diff --git a/src/hvpp/hvpp/hvpp.cpp b/src/hvpp/hvpp/hvpp.cpp
index f8b66fd..7e0177a 100644
--- a/src/hvpp/hvpp/hvpp.cpp
+++ b/src/hvpp/hvpp/hvpp.cpp
@@ -90,6 +90,25 @@ HvppEptMapIdentityEx(
   ept_->map_identity((epte_t::access_type)(Access));
 }
 
+VOID
+NTAPI
+HvppEptMapIdentitySparse(
+  _In_ PEPT Ept
+  )
+{
+  ept_->map_identity_sparse();
+}
+
+VOID
+NTAPI
+HvppEptMapIdentitySparseEx(
+  _In_ PEPT Ept,
+  _In_ ULONG Access
+  )
+{
+  ept_->map_identity_sparse((epte_t::access_type)(Access));
+}
+
 PEPTE
 NTAPI
 HvppEptMap(
diff --git a/src/hvpp/hvpp/hvpp.h b/src/hvpp/hvpp/hvpp.h
index 01ad351..823c0e5 100644
--- a/src/hvpp/hvpp/hvpp.h
+++ b/src/hvpp/hvpp/hvpp.h
@@ -1197,6 +1197,19 @@ HvppEptMapIdentityEx(
   _In_ ULONG Access
   );
 
+VOID
+NTAPI
+HvppEptMapIdentitySparse(
+  _In_ PEPT Ept
+  );
+
+VOID
+NTAPI
+HvppEptMapIdentitySparseEx(
+  _In_ PEPT Ept,
+  _In_ ULONG Access
+  );
+
 PEPTE
 NTAPI
 HvppEptMap(