linux-kernel - [PATCH 03/10] KVM: SVM: Drop pointless masking of kernel page pa's with "AVIC's" HPA mask

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Message-ID: <20230815213533.548732-4-seanjc@google.com>
Date:   Tue, 15 Aug 2023 14:35:26 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Joerg Roedel <joro@...tes.org>
Cc:     kvm@...r.kernel.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH 03/10] KVM: SVM: Drop pointless masking of kernel page pa's
 with "AVIC's" HPA mask

Drop AVIC_HPA_MASK and all its users, the mask is just the 4KiB-aligned
maximum theoretical physical address for x86-64 CPUs.  All usage in KVM
masks the result of page_to_phys(), which on x86-64 is guaranteed to be
4KiB aligned and a legal physical address; if either of those requirements
doesn't hold true, KVM has far bigger problems.

The unnecessarily masking in avic_init_vmcb() also incorrectly assumes
that SME's C-bit resides between bits 51:11; that holds true for current
CPUs, but isn't required by AMD's architecture:

  In some implementations, the bit used may be a physical address bit

Key word being "may".

Opportunistically use the GENMASK_ULL() version for
AVIC_PHYSICAL_ID_ENTRY_BACKING_PAGE_MASK, which is far more readable
than a set of repeating Fs.  Keep the macro even though it's unused, and
will likely never be used, as it helps visualize the layout of an entry.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/include/asm/svm.h |  6 +-----
 arch/x86/kvm/svm/avic.c    | 11 +++++------
 2 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
index 609c9b596399..df644ca3febe 100644
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -250,7 +250,7 @@ struct __attribute__ ((__packed__)) vmcb_control_area {
 #define AVIC_LOGICAL_ID_ENTRY_VALID_MASK		(1 << 31)
 
 #define AVIC_PHYSICAL_ID_ENTRY_HOST_PHYSICAL_ID_MASK	GENMASK_ULL(11, 0)
-#define AVIC_PHYSICAL_ID_ENTRY_BACKING_PAGE_MASK	(0xFFFFFFFFFFULL << 12)
+#define AVIC_PHYSICAL_ID_ENTRY_BACKING_PAGE_MASK	GENMASK_ULL(51, 12)
 #define AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK		(1ULL << 62)
 #define AVIC_PHYSICAL_ID_ENTRY_VALID_MASK		(1ULL << 63)
 #define AVIC_PHYSICAL_ID_TABLE_SIZE_MASK		(0xFFULL)
@@ -284,10 +284,6 @@ enum avic_ipi_failure_cause {
 static_assert((AVIC_MAX_PHYSICAL_ID & AVIC_PHYSICAL_MAX_INDEX_MASK) == AVIC_MAX_PHYSICAL_ID);
 static_assert((X2AVIC_MAX_PHYSICAL_ID & AVIC_PHYSICAL_MAX_INDEX_MASK) == X2AVIC_MAX_PHYSICAL_ID);
 
-#define AVIC_HPA_MASK	~((0xFFFULL << 52) | 0xFFF)
-static_assert(AVIC_PHYSICAL_ID_ENTRY_BACKING_PAGE_MASK == AVIC_HPA_MASK);
-static_assert(AVIC_PHYSICAL_ID_ENTRY_BACKING_PAGE_MASK == GENMASK_ULL(51, 12));
-
 #define SVM_SEV_FEAT_DEBUG_SWAP                        BIT(5)
 
 struct vmcb_seg {
diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 442c58ef8158..b8313f2d88fa 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -248,9 +248,9 @@ void avic_init_vmcb(struct vcpu_svm *svm, struct vmcb *vmcb)
 	phys_addr_t lpa = __sme_set(page_to_phys(kvm_svm->avic_logical_id_table_page));
 	phys_addr_t ppa = __sme_set(page_to_phys(kvm_svm->avic_physical_id_table_page));
 
-	vmcb->control.avic_backing_page = bpa & AVIC_HPA_MASK;
-	vmcb->control.avic_logical_id = lpa & AVIC_HPA_MASK;
-	vmcb->control.avic_physical_id = ppa & AVIC_HPA_MASK;
+	vmcb->control.avic_backing_page = bpa;
+	vmcb->control.avic_logical_id = lpa;
+	vmcb->control.avic_physical_id = ppa;
 	vmcb->control.avic_vapic_bar = APIC_DEFAULT_PHYS_BASE;
 
 	if (kvm_apicv_activated(svm->vcpu.kvm))
@@ -308,7 +308,7 @@ static int avic_init_backing_page(struct kvm_vcpu *vcpu)
 	if (!entry)
 		return -EINVAL;
 
-	new_entry = __sme_set(page_to_phys(svm->avic_backing_page) & AVIC_HPA_MASK) |
+	new_entry = __sme_set(page_to_phys(svm->avic_backing_page)) |
 		    AVIC_PHYSICAL_ID_ENTRY_VALID_MASK;
 	WRITE_ONCE(*entry, new_entry);
 
@@ -917,8 +917,7 @@ int avic_pi_update_irte(struct kvm *kvm, unsigned int host_irq,
 			struct amd_iommu_pi_data pi;
 
 			/* Try to enable guest_mode in IRTE */
-			pi.base = __sme_set(page_to_phys(svm->avic_backing_page) &
-					    AVIC_HPA_MASK);
+			pi.base = __sme_set(page_to_phys(svm->avic_backing_page));
 			pi.ga_tag = AVIC_GATAG(to_kvm_svm(kvm)->avic_vm_id,
 						     svm->vcpu.vcpu_id);
 			pi.is_guest_mode = true;
-- 
2.41.0.694.ge786442a9b-goog