linux-kernel - [RFC PATCH v5 053/104] KVM: x86/mmu: steal software usable bit for EPT to represent shared page

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Message-Id: <028675e255cb2a23186ebc7a94c06a47375c6883.1646422845.git.isaku.yamahata@intel.com>
Date:   Fri,  4 Mar 2022 11:49:09 -0800
From:   isaku.yamahata@...el.com
To:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     isaku.yamahata@...el.com, isaku.yamahata@...il.com,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>, erdemaktas@...gle.com,
        Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: [RFC PATCH v5 053/104] KVM: x86/mmu: steal software usable bit for EPT to represent shared page

From: Isaku Yamahata <isaku.yamahata@...el.com>

With TDX, all GFNs are private at guest boot time.  At run time guest TD
can explicitly change it to shared from private or vice-versa by MapGPA
hypercall.  If it's specified, the given GFN can't be used as otherwise.
That's is, if a guest tells KVM that the GFN is shared, it can't be used
as private.  or vice-versa.

KVM needs to record it.  Steal software usable bit for it from MMIO
counter.

Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
---
 arch/x86/kvm/mmu/spte.h | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
index e88f796724b4..25dffdb488d1 100644
--- a/arch/x86/kvm/mmu/spte.h
+++ b/arch/x86/kvm/mmu/spte.h
@@ -14,6 +14,9 @@
  */
 #define SPTE_MMU_PRESENT_MASK		BIT_ULL(11)
 
+/* Masks that used to track for shared GPA **/
+#define SPTE_PRIVATE_PROHIBIT	BIT_ULL(62)
+
 /*
  * TDP SPTES (more specifically, EPT SPTEs) may not have A/D bits, and may also
  * be restricted to using write-protection (for L2 when CPU dirty logging, i.e.
@@ -124,7 +127,7 @@ static_assert(!(EPT_SPTE_MMU_WRITABLE & SHADOW_ACC_TRACK_SAVED_MASK));
  * the memslots generation and is derived as follows:
  *
  * Bits 0-7 of the MMIO generation are propagated to spte bits 3-10
- * Bits 8-18 of the MMIO generation are propagated to spte bits 52-62
+ * Bits 8-18 of the MMIO generation are propagated to spte bits 52-61
  *
  * The KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS flag is intentionally not included in
  * the MMIO generation number, as doing so would require stealing a bit from
@@ -138,7 +141,7 @@ static_assert(!(EPT_SPTE_MMU_WRITABLE & SHADOW_ACC_TRACK_SAVED_MASK));
 #define MMIO_SPTE_GEN_LOW_END		10
 
 #define MMIO_SPTE_GEN_HIGH_START	52
-#define MMIO_SPTE_GEN_HIGH_END		62
+#define MMIO_SPTE_GEN_HIGH_END		61
 
 #define MMIO_SPTE_GEN_LOW_MASK		GENMASK_ULL(MMIO_SPTE_GEN_LOW_END, \
 						    MMIO_SPTE_GEN_LOW_START)
@@ -151,7 +154,7 @@ static_assert(!(SPTE_MMU_PRESENT_MASK &
 #define MMIO_SPTE_GEN_HIGH_BITS		(MMIO_SPTE_GEN_HIGH_END - MMIO_SPTE_GEN_HIGH_START + 1)
 
 /* remember to adjust the comment above as well if you change these */
-static_assert(MMIO_SPTE_GEN_LOW_BITS == 8 && MMIO_SPTE_GEN_HIGH_BITS == 11);
+static_assert(MMIO_SPTE_GEN_LOW_BITS == 8 && MMIO_SPTE_GEN_HIGH_BITS == 10);
 
 #define MMIO_SPTE_GEN_LOW_SHIFT		(MMIO_SPTE_GEN_LOW_START - 0)
 #define MMIO_SPTE_GEN_HIGH_SHIFT	(MMIO_SPTE_GEN_HIGH_START - MMIO_SPTE_GEN_LOW_BITS)
@@ -208,6 +211,7 @@ extern u64 __read_mostly shadow_nonpresent_or_rsvd_mask;
 
 /* Removed SPTEs must not be misconstrued as shadow present PTEs. */
 static_assert(!(REMOVED_SPTE & SPTE_MMU_PRESENT_MASK));
+static_assert(!(REMOVED_SPTE & SPTE_PRIVATE_PROHIBIT));
 
 /*
  * See above comment around REMOVED_SPTE.  SHADOW_REMOVED_SPTE is the actual
@@ -222,6 +226,11 @@ static inline bool is_removed_spte(u64 spte)
 	return spte == SHADOW_REMOVED_SPTE;
 }
 
+static inline bool is_private_prohibit_spte(u64 spte)
+{
+	return !!(spte & SPTE_PRIVATE_PROHIBIT);
+}
+
 /*
  * In some cases, we need to preserve the GFN of a non-present or reserved
  * SPTE when we usurp the upper five bits of the physical address space to
-- 
2.25.1