linux-kernel - [PATCH v11 031/113] KVM: x86/mmu: Allow non-zero value for non-present SPTE and removed SPTE

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Message-Id: <d193421197cb7699d5eee09b72e6ba92e9978a7b.1673539699.git.isaku.yamahata@intel.com>
Date:   Thu, 12 Jan 2023 08:31:39 -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>, erdemaktas@...gle.com,
        Sean Christopherson <seanjc@...gle.com>,
        Sagi Shahar <sagis@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: [PATCH v11 031/113] KVM: x86/mmu: Allow non-zero value for non-present SPTE and removed SPTE

From: Sean Christopherson <sean.j.christopherson@...el.com>

For TD guest, the current way to emulate MMIO doesn't work any more, as KVM
is not able to access the private memory of TD guest and do the emulation.
Instead, TD guest expects to receive #VE when it accesses the MMIO and then
it can explicitly make hypercall to KVM to get the expected information.

To achieve this, the TDX module always enables "EPT-violation #VE" in the
VMCS control.  And accordingly, for the MMIO spte for the shared GPA,
1. KVM needs to set "suppress #VE" bit for the non-present SPTE so that EPT
violation happens on TD accessing MMIO range.  2. On EPT violation, KVM
sets the MMIO spte to clear "suppress #VE" bit so the TD guest can receive
the #VE instead of EPT misconfigration unlike VMX case.  For the shared GPA
that is not populated yet, EPT violation need to be triggered when TD guest
accesses such shared GPA.  The non-present SPTE value for shared GPA should
set "suppress #VE" bit.

Add "suppress #VE" bit (bit 63) to SHADOW_NONPRESENT_VALUE and
REMOVED_SPTE.  Unconditionally set the "suppress #VE" bit (which is bit 63)
for both AMD and Intel as: 1) AMD hardware doesn't use this bit when
present bit is off; 2) for normal VMX guest, KVM never enables the
"EPT-violation #VE" in VMCS control and "suppress #VE" bit is ignored by
hardware.

Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
---
 arch/x86/include/asm/vmx.h |  1 +
 arch/x86/kvm/mmu/spte.h    | 15 ++++++++++++++-
 arch/x86/kvm/mmu/tdp_mmu.c |  8 ++++++++
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
index 498dc600bd5c..cdbf12c1a83c 100644
--- a/arch/x86/include/asm/vmx.h
+++ b/arch/x86/include/asm/vmx.h
@@ -511,6 +511,7 @@ enum vmcs_field {
 #define VMX_EPT_IPAT_BIT    			(1ull << 6)
 #define VMX_EPT_ACCESS_BIT			(1ull << 8)
 #define VMX_EPT_DIRTY_BIT			(1ull << 9)
+#define VMX_EPT_SUPPRESS_VE_BIT			(1ull << 63)
 #define VMX_EPT_RWX_MASK                        (VMX_EPT_READABLE_MASK |       \
 						 VMX_EPT_WRITABLE_MASK |       \
 						 VMX_EPT_EXECUTABLE_MASK)
diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
index f190eaf6b2b5..471378ee9071 100644
--- a/arch/x86/kvm/mmu/spte.h
+++ b/arch/x86/kvm/mmu/spte.h
@@ -148,7 +148,20 @@ static_assert(MMIO_SPTE_GEN_LOW_BITS == 8 && MMIO_SPTE_GEN_HIGH_BITS == 11);
 
 #define MMIO_SPTE_GEN_MASK		GENMASK_ULL(MMIO_SPTE_GEN_LOW_BITS + MMIO_SPTE_GEN_HIGH_BITS - 1, 0)
 
+/*
+ * Non-present SPTE value for both VMX and SVM for TDP MMU.
+ * For SVM NPT, for non-present spte (bit 0 = 0), other bits are ignored.
+ * For VMX EPT, bit 63 is ignored if #VE is disabled. (EPT_VIOLATION_VE=0)
+ *              bit 63 is #VE suppress if #VE is enabled. (EPT_VIOLATION_VE=1)
+ * For TDX:
+ *   TDX module sets EPT_VIOLATION_VE for Secure-EPT and conventional EPT
+ */
+#ifdef CONFIG_X86_64
+#define SHADOW_NONPRESENT_VALUE	BIT_ULL(63)
+static_assert(!(SHADOW_NONPRESENT_VALUE & SPTE_MMU_PRESENT_MASK));
+#else
 #define SHADOW_NONPRESENT_VALUE	0ULL
+#endif
 
 extern u64 __read_mostly shadow_host_writable_mask;
 extern u64 __read_mostly shadow_mmu_writable_mask;
@@ -195,7 +208,7 @@ extern u64 __read_mostly shadow_nonpresent_or_rsvd_mask;
  *
  * Only used by the TDP MMU.
  */
-#define REMOVED_SPTE	0x5a0ULL
+#define REMOVED_SPTE	(SHADOW_NONPRESENT_VALUE | 0x5a0ULL)
 
 /* Removed SPTEs must not be misconstrued as shadow present PTEs. */
 static_assert(!(REMOVED_SPTE & SPTE_MMU_PRESENT_MASK));
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 9cf5844dd34a..6111e3e9266d 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -700,6 +700,14 @@ static inline int tdp_mmu_zap_spte_atomic(struct kvm *kvm,
 	 * overwrite the special removed SPTE value. No bookkeeping is needed
 	 * here since the SPTE is going from non-present to non-present.  Use
 	 * the raw write helper to avoid an unnecessary check on volatile bits.
+	 *
+	 * Set non-present value to SHADOW_NONPRESENT_VALUE, rather than 0.
+	 * It is because when TDX is enabled, TDX module always
+	 * enables "EPT-violation #VE", so KVM needs to set
+	 * "suppress #VE" bit in EPT table entries, in order to get
+	 * real EPT violation, rather than TDVMCALL.  KVM sets
+	 * SHADOW_NONPRESENT_VALUE (which sets "suppress #VE" bit) so it
+	 * can be set when EPT table entries are zapped.
 	 */
 	__kvm_tdp_mmu_write_spte(iter->sptep, SHADOW_NONPRESENT_VALUE);
 
-- 
2.25.1