linux-kernel - [PATCH 7/7] KVM: TDX: Add TSX_CTRL msr into uret

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Message-ID: <20241121201448.36170-8-adrian.hunter@intel.com>
Date: Thu, 21 Nov 2024 22:14:46 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: pbonzini@...hat.com,
	seanjc@...gle.com,
	kvm@...r.kernel.org,
	dave.hansen@...ux.intel.com
Cc: rick.p.edgecombe@...el.com,
	kai.huang@...el.com,
	adrian.hunter@...el.com,
	reinette.chatre@...el.com,
	xiaoyao.li@...el.com,
	tony.lindgren@...ux.intel.com,
	binbin.wu@...ux.intel.com,
	dmatlack@...gle.com,
	isaku.yamahata@...el.com,
	nik.borisov@...e.com,
	linux-kernel@...r.kernel.org,
	x86@...nel.org,
	yan.y.zhao@...el.com,
	chao.gao@...el.com,
	weijiang.yang@...el.com
Subject: [PATCH 7/7] KVM: TDX: Add TSX_CTRL msr into uret_msrs list

From: Yang Weijiang <weijiang.yang@...el.com>

TDX module resets the TSX_CTRL MSR to 0 at TD exit if TSX is enabled for
TD. Or it preserves the TSX_CTRL MSR if TSX is disabled for TD.  VMM can
rely on uret_msrs mechanism to defer the reload of host value until exiting
to user space.

Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
---
TD vcpu enter/exit v1:
 - Update from rename in earlier patches (Binbin)

v19:
- fix the type of tdx_uret_tsx_ctrl_slot. unguent int => int.
---
 arch/x86/kvm/vmx/tdx.c | 33 +++++++++++++++++++++++++++++++--
 arch/x86/kvm/vmx/tdx.h |  8 ++++++++
 2 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 4a33ca54c8ba..2c7b6308da73 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -722,14 +722,21 @@ static struct tdx_uret_msr tdx_uret_msrs[] = {
 	{.msr = MSR_LSTAR,},
 	{.msr = MSR_TSC_AUX,},
 };
+static int tdx_uret_tsx_ctrl_slot;
 
-static void tdx_user_return_msr_update_cache(void)
+static void tdx_user_return_msr_update_cache(struct kvm_vcpu *vcpu)
 {
 	int i;
 
 	for (i = 0; i < ARRAY_SIZE(tdx_uret_msrs); i++)
 		kvm_user_return_msr_update_cache(tdx_uret_msrs[i].slot,
 						 tdx_uret_msrs[i].defval);
+	/*
+	 * TSX_CTRL is reset to 0 if guest TSX is supported. Otherwise
+	 * preserved.
+	 */
+	if (to_kvm_tdx(vcpu->kvm)->tsx_supported && tdx_uret_tsx_ctrl_slot != -1)
+		kvm_user_return_msr_update_cache(tdx_uret_tsx_ctrl_slot, 0);
 }
 
 static void tdx_restore_host_xsave_state(struct kvm_vcpu *vcpu)
@@ -817,7 +824,7 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
 
 	tdx_vcpu_enter_exit(vcpu);
 
-	tdx_user_return_msr_update_cache();
+	tdx_user_return_msr_update_cache(vcpu);
 	tdx_restore_host_xsave_state(vcpu);
 	tdx->host_state_need_restore = true;
 
@@ -1258,6 +1265,22 @@ static int setup_tdparams_cpuids(struct kvm_cpuid2 *cpuid,
 	return 0;
 }
 
+static bool tdparams_tsx_supported(struct kvm_cpuid2 *cpuid)
+{
+	const struct kvm_cpuid_entry2 *entry;
+	u64 mask;
+	u32 ebx;
+
+	entry = kvm_find_cpuid_entry2(cpuid->entries, cpuid->nent, 0x7, 0);
+	if (entry)
+		ebx = entry->ebx;
+	else
+		ebx = 0;
+
+	mask = __feature_bit(X86_FEATURE_HLE) | __feature_bit(X86_FEATURE_RTM);
+	return ebx & mask;
+}
+
 static int setup_tdparams(struct kvm *kvm, struct td_params *td_params,
 			struct kvm_tdx_init_vm *init_vm)
 {
@@ -1299,6 +1322,7 @@ static int setup_tdparams(struct kvm *kvm, struct td_params *td_params,
 	MEMCPY_SAME_SIZE(td_params->mrowner, init_vm->mrowner);
 	MEMCPY_SAME_SIZE(td_params->mrownerconfig, init_vm->mrownerconfig);
 
+	to_kvm_tdx(kvm)->tsx_supported = tdparams_tsx_supported(cpuid);
 	return 0;
 }
 
@@ -2272,6 +2296,11 @@ static int __init __tdx_bringup(void)
 			return -EIO;
 		}
 	}
+	tdx_uret_tsx_ctrl_slot = kvm_find_user_return_msr(MSR_IA32_TSX_CTRL);
+	if (tdx_uret_tsx_ctrl_slot == -1 && boot_cpu_has(X86_FEATURE_MSR_TSX_CTRL)) {
+		pr_err("MSR_IA32_TSX_CTRL isn't included by kvm_find_user_return_msr\n");
+		return -EIO;
+	}
 
 	/*
 	 * Enabling TDX requires enabling hardware virtualization first,
diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h
index 48cf0a1abfcc..815ff6bdbc7e 100644
--- a/arch/x86/kvm/vmx/tdx.h
+++ b/arch/x86/kvm/vmx/tdx.h
@@ -29,6 +29,14 @@ struct kvm_tdx {
 	u8 nr_tdcs_pages;
 	u8 nr_vcpu_tdcx_pages;
 
+	/*
+	 * Used on each TD-exit, see tdx_user_return_msr_update_cache().
+	 * TSX_CTRL value on TD exit
+	 * - set 0     if guest TSX enabled
+	 * - preserved if guest TSX disabled
+	 */
+	bool tsx_supported;
+
 	u64 tsc_offset;
 
 	enum kvm_tdx_state state;
-- 
2.43.0