linux-kernel - [PATCH] KVM: SVM: Remove TSS reloading code after VMEXIT

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Message-ID: <20230518170653.704562-1-mizhang@google.com>
Date:   Thu, 18 May 2023 17:06:53 +0000
From:   Mingwei Zhang <mizhang@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     "H. Peter Anvin" <hpa@...or.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Venkatesh Srinivas <venkateshs@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Mingwei Zhang <mizhang@...gle.com>
Subject: [PATCH] KVM: SVM: Remove TSS reloading code after VMEXIT

Remove TSS reloading code after VMEXIT since upstream KVM after [1] has
already been using VMLOAD to load host segment state (including TSS).
Therefore, reload_tss() becomes redundant. Because of that, also remove the
relevant data field tss_desc in svm_cpu_data as well as its data structure
definition.

[1] commit e79b91bb3c91 ("KVM: SVM: use vmsave/vmload for saving/restoring additionalhost state")

Reported-by: Venkatesh Srinivas <venkateshs@...gle.com>
Suggested-by: Jim Mattson <jmattson@...gle.com>
Tested-by: Mingwei Zhang <mizhang@...gle.com>
Signed-off-by: Mingwei Zhang <mizhang@...gle.com>
---
 arch/x86/kvm/svm/svm.c | 24 ------------------------
 arch/x86/kvm/svm/svm.h |  1 -
 2 files changed, 25 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index eb308c9994f9..cfbe00360908 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -240,15 +240,6 @@ static u8 rsm_ins_bytes[] = "\x0f\xaa";
 
 static unsigned long iopm_base;
 
-struct kvm_ldttss_desc {
-	u16 limit0;
-	u16 base0;
-	unsigned base1:8, type:5, dpl:2, p:1;
-	unsigned limit1:4, zero0:3, g:1, base2:8;
-	u32 base3;
-	u32 zero1;
-} __attribute__((packed));
-
 DEFINE_PER_CPU(struct svm_cpu_data, svm_data);
 
 /*
@@ -584,7 +575,6 @@ static int svm_hardware_enable(void)
 
 	struct svm_cpu_data *sd;
 	uint64_t efer;
-	struct desc_struct *gdt;
 	int me = raw_smp_processor_id();
 
 	rdmsrl(MSR_EFER, efer);
@@ -597,9 +587,6 @@ static int svm_hardware_enable(void)
 	sd->next_asid = sd->max_asid + 1;
 	sd->min_asid = max_sev_asid + 1;
 
-	gdt = get_current_gdt_rw();
-	sd->tss_desc = (struct kvm_ldttss_desc *)(gdt + GDT_ENTRY_TSS);
-
 	wrmsrl(MSR_EFER, efer | EFER_SVME);
 
 	wrmsrl(MSR_VM_HSAVE_PA, sd->save_area_pa);
@@ -3453,14 +3440,6 @@ static int svm_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
 	return svm_invoke_exit_handler(vcpu, exit_code);
 }
 
-static void reload_tss(struct kvm_vcpu *vcpu)
-{
-	struct svm_cpu_data *sd = per_cpu_ptr(&svm_data, vcpu->cpu);
-
-	sd->tss_desc->type = 9; /* available 32/64-bit TSS */
-	load_TR_desc();
-}
-
 static void pre_svm_run(struct kvm_vcpu *vcpu)
 {
 	struct svm_cpu_data *sd = per_cpu_ptr(&svm_data, vcpu->cpu);
@@ -4064,9 +4043,6 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
 
 	svm_vcpu_enter_exit(vcpu, spec_ctrl_intercepted);
 
-	if (!sev_es_guest(vcpu->kvm))
-		reload_tss(vcpu);
-
 	if (!static_cpu_has(X86_FEATURE_V_SPEC_CTRL))
 		x86_spec_ctrl_restore_host(svm->virt_spec_ctrl);
 
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index f44751dd8d5d..18af7e712a5a 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -303,7 +303,6 @@ struct svm_cpu_data {
 	u32 max_asid;
 	u32 next_asid;
 	u32 min_asid;
-	struct kvm_ldttss_desc *tss_desc;
 
 	struct page *save_area;
 	unsigned long save_area_pa;
-- 
2.40.1.698.g37aff9b760-goog