linux-kernel - [PATCH V2 09/12] KVM: TDX: restore user ret MSRs

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Message-ID: <20250129095902.16391-10-adrian.hunter@intel.com>
Date: Wed, 29 Jan 2025 11:58:58 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: pbonzini@...hat.com,
	seanjc@...gle.com
Cc: kvm@...r.kernel.org,
	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,
	yan.y.zhao@...el.com,
	chao.gao@...el.com,
	weijiang.yang@...el.com
Subject: [PATCH V2 09/12] KVM: TDX: restore user ret MSRs

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

Several user ret MSRs are clobbered on TD exit.  Restore those values on
TD exit and before returning to ring 3.

Co-developed-by: Tony Lindgren <tony.lindgren@...ux.intel.com>
Signed-off-by: Tony Lindgren <tony.lindgren@...ux.intel.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
---
TD vcpu enter/exit v2:
 - No changes

TD vcpu enter/exit v1:
 - Rename tdx_user_return_update_cache() ->
     tdx_user_return_msr_update_cache() (extrapolated from Binbin)
 - Adjust to rename in previous patches (Binbin)
 - Simplify comment (Tony)
 - Move code change in tdx_hardware_setup() to __tdx_bringup().
---
 arch/x86/kvm/vmx/tdx.c | 44 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 43 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index e4355553569a..a0f5cdfd290b 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -729,6 +729,28 @@ int tdx_vcpu_pre_run(struct kvm_vcpu *vcpu)
 	return 1;
 }
 
+struct tdx_uret_msr {
+	u32 msr;
+	unsigned int slot;
+	u64 defval;
+};
+
+static struct tdx_uret_msr tdx_uret_msrs[] = {
+	{.msr = MSR_SYSCALL_MASK, .defval = 0x20200 },
+	{.msr = MSR_STAR,},
+	{.msr = MSR_LSTAR,},
+	{.msr = MSR_TSC_AUX,},
+};
+
+static void tdx_user_return_msr_update_cache(void)
+{
+	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);
+}
+
 static bool tdx_guest_state_is_invalid(struct kvm_vcpu *vcpu)
 {
 	struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm);
@@ -784,6 +806,8 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
 
 	tdx_vcpu_enter_exit(vcpu);
 
+	tdx_user_return_msr_update_cache();
+
 	kvm_load_host_xsave_state(vcpu);
 
 	vcpu->arch.regs_avail &= ~TDX_REGS_UNSUPPORTED_SET;
@@ -2245,7 +2269,25 @@ static bool __init kvm_can_support_tdx(void)
 static int __init __tdx_bringup(void)
 {
 	const struct tdx_sys_info_td_conf *td_conf;
-	int r;
+	int r, i;
+
+	for (i = 0; i < ARRAY_SIZE(tdx_uret_msrs); i++) {
+		/*
+		 * Check if MSRs (tdx_uret_msrs) can be saved/restored
+		 * before returning to user space.
+		 *
+		 * this_cpu_ptr(user_return_msrs)->registered isn't checked
+		 * because the registration is done at vcpu runtime by
+		 * tdx_user_return_msr_update_cache().
+		 */
+		tdx_uret_msrs[i].slot = kvm_find_user_return_msr(tdx_uret_msrs[i].msr);
+		if (tdx_uret_msrs[i].slot == -1) {
+			/* If any MSR isn't supported, it is a KVM bug */
+			pr_err("MSR %x isn't included by kvm_find_user_return_msr\n",
+				tdx_uret_msrs[i].msr);
+			return -EIO;
+		}
+	}
 
 	/*
 	 * Enabling TDX requires enabling hardware virtualization first,
-- 
2.43.0