From nobody Sat Oct 4 01:43:18 2025 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B67762EAB71; Thu, 21 Aug 2025 22:37:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755815883; cv=none; b=S4OrjGvH4aJyr5K/lAHFmJ6eW3YazsOREnDibZ4V69b1CSf7sp28d8EUB7Q+sNvpLpAMSqS+5uk8JMttD1e/lwSyBxOFSXZULS8yE9jvPPuS3BBPMJ9n6hA4jKZDgGMhde1pkfaasHFzXlQpFILazcGWTY+18Fig7PtWZa/CuHU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755815883; c=relaxed/simple; bh=Z99PJAD2vMkzajGMq6ivX2aPlJ7mPAJ9k4cGnTty2/o=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=DRaXcd66XhhWl9Q2Sl4X3gmeC1qZXTlKuAbzrTU2XF/prFEfXSKD2zjP6Yol4uQ5qDOlBGCkdmbJz3/1Tp4jWi/q38Z7mR37vD12YoOvLI/RbN2HLHNPY92k5H+2MJwNaFrNwAb9XUeVYRjayvbYEDPOVcQB4WCNMe5X2GL8piA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com; spf=pass smtp.mailfrom=zytor.com; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b=mwMdNyx0; arc=none smtp.client-ip=198.137.202.136 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zytor.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="mwMdNyx0" Received: from terminus.zytor.com (terminus.zytor.com [IPv6:2607:7c80:54:3:0:0:0:136]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 57LMaUOV984441 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Thu, 21 Aug 2025 15:36:47 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 57LMaUOV984441 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2025072201; t=1755815808; bh=b1ixQ5NuJEx+fGpQPFeEarfOwlWVbb2VBVcYCcjWErg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=mwMdNyx0fll8l4aONGZm4Bz1za2B27C9kaAIq79eezjqwY/U3JMUr593XfpWW8hrh SHkh+JQZ2EeqN960Oq3nqUa4PfZ991M6C/nVJX3nVLqLE+46F75N5gYeu54Ff/HkA+ emv/ftkJODM9CJANa44mg7kdiydyA3OD4mq4Oa+vRUVmLLv3lRv3MOOt76BrIo2NUS jhy34z4hjw+oMAn2fAu1yU1jJygOf1JW0nTvTqYysu1Blqr12BgrGDrNWP5x2OYdoz 3ujeHVBgnXG20AfwmY7G4ZllCLaYTwjqUcX94n0w2qr7ZkXGpthG7s+g4T5xmbc/sN tDSzL+Re6EYHQ== From: "Xin Li (Intel)" To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org Cc: pbonzini@redhat.com, seanjc@google.com, corbet@lwn.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, xin@zytor.com, luto@kernel.org, peterz@infradead.org, andrew.cooper3@citrix.com, chao.gao@intel.com, hch@infradead.org Subject: [PATCH v6 07/20] KVM: VMX: Save/restore guest FRED RSP0 Date: Thu, 21 Aug 2025 15:36:16 -0700 Message-ID: <20250821223630.984383-8-xin@zytor.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250821223630.984383-1-xin@zytor.com> References: <20250821223630.984383-1-xin@zytor.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Xin Li Save guest FRED RSP0 in vmx_prepare_switch_to_host() and restore it in vmx_prepare_switch_to_guest() because MSR_IA32_FRED_RSP0 is passed through to the guest, thus is volatile/unknown. Note, host FRED RSP0 is restored in arch_exit_to_user_mode_prepare(), regardless of whether it is modified in KVM. Signed-off-by: Xin Li Signed-off-by: Xin Li (Intel) Tested-by: Shan Kang Tested-by: Xuelian Guo --- Changes in v5: * Remove the cpu_feature_enabled() check when set/get guest MSR_IA32_FRED_RSP0, as guest_cpu_cap_has() should suffice (Sean). * Add a comment when synchronizing current MSR_IA32_FRED_RSP0 MSR to the kernel's local cache, because its handling is different from the MSR_KERNEL_GS_BASE handling (Sean). * Add TB from Xuelian Guo. Changes in v3: * KVM only needs to save/restore guest FRED RSP0 now as host FRED RSP0 is restored in arch_exit_to_user_mode_prepare() (Sean Christopherson). Changes in v2: * Don't use guest_cpuid_has() in vmx_prepare_switch_to_{host,guest}(), which are called from IRQ-disabled context (Chao Gao). * Reset msr_guest_fred_rsp0 in __vmx_vcpu_reset() (Chao Gao). --- arch/x86/kvm/vmx/vmx.c | 14 ++++++++++++++ arch/x86/kvm/vmx/vmx.h | 1 + 2 files changed, 15 insertions(+) diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 8e81230be7af..714de55f4e8b 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -1293,6 +1293,10 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vc= pu) } =20 wrmsrq(MSR_KERNEL_GS_BASE, vmx->msr_guest_kernel_gs_base); + + if (guest_cpu_cap_has(vcpu, X86_FEATURE_FRED)) + wrmsrns(MSR_IA32_FRED_RSP0, vmx->msr_guest_fred_rsp0); + #else savesegment(fs, fs_sel); savesegment(gs, gs_sel); @@ -1337,6 +1341,16 @@ static void vmx_prepare_switch_to_host(struct vcpu_v= mx *vmx) invalidate_tss_limit(); #ifdef CONFIG_X86_64 wrmsrq(MSR_KERNEL_GS_BASE, vmx->vt.msr_host_kernel_gs_base); + + if (guest_cpu_cap_has(&vmx->vcpu, X86_FEATURE_FRED)) { + vmx->msr_guest_fred_rsp0 =3D read_msr(MSR_IA32_FRED_RSP0); + /* + * Synchronize the current value in hardware to the kernel's + * local cache. The desired host RSP0 will be set when the + * CPU exits to userspace (RSP0 is a per-task value). + */ + fred_sync_rsp0(vmx->msr_guest_fred_rsp0); + } #endif load_fixmap_gdt(raw_smp_processor_id()); vmx->vt.guest_state_loaded =3D false; diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h index e577af1003d8..733fa2ef4bea 100644 --- a/arch/x86/kvm/vmx/vmx.h +++ b/arch/x86/kvm/vmx/vmx.h @@ -227,6 +227,7 @@ struct vcpu_vmx { bool guest_uret_msrs_loaded; #ifdef CONFIG_X86_64 u64 msr_guest_kernel_gs_base; + u64 msr_guest_fred_rsp0; #endif =20 u64 spec_ctrl; --=20 2.50.1