From nobody Fri Oct 3 15:32:57 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 F10D0321F26; Fri, 29 Aug 2025 15:33:08 +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=1756481592; cv=none; b=TkRgHu5VeOOcQ6WkisLolGsw7k/dq0PMGIo5RpnoJbzRJgyJl9LPfVLXmC8NktVDWmrBakhjZibvSyw4I/ADlXECTObhTs1yIOsgebZTkk0OBpsPI+6Z0ij0G8AkptL5mCY0Xby0t03A9jUqvnXPvrhazE3q33kw9WWD5KqJktA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756481592; c=relaxed/simple; bh=B+m/8qllmHVTlj/AM37AJiiUWBYT48rw46oDultWBPo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=nx7a0rxda9VUWI2HHi48tQpeBf/eZS1utkYGyvhmz/WPfU/994i6PVe54qTPl6qYzRk3qinlaxZ0J9xDfEsKE9bDPV430wzHI0qleJZCKXsq1g1MipxxL9FUmF9dUhoG+IcjLTneL8bF7e2Uk0vN5GIDsJC4+UK93vmWWAZ7y/4= 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=bWcGNT/Z; 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="bWcGNT/Z" 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 57TFVo4E2871953 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Fri, 29 Aug 2025 08:32:19 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 57TFVo4E2871953 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2025082201; t=1756481540; bh=bvBHvjul1GobdicSx2txFw5fgQ8wUMiarsYtlt6XWY4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bWcGNT/ZCkVvaDiyN0n7t4aRTwIleF7m6yMZ52/htAc/ffzypnMVINfmqiyYHTbxP Pa/GxNTnt3HYNsy5ujNp5op9TqQLd+UJNa671y9ZvOEuXH+lMZO5ld8XpKz3DENu+i lUkMpBwh2hq/iOvW+9/KK4+Sxan4yPyz1atRerF8EE1MeYA3FGn4UQr3+RsI42Gztz qiyMRVuiCtGAIJ0GxTwyK/e5MFLVg4FLBGmaKZbVk9Bg8jfjm9ddBOCfTcRgbmGNbp B2Q7Bgjonr1WaNhXtZa+0X9GPFav4/94Ud5/AiEBYVzA8BsF5//TVAYFzlZ5pygcYf 9OlMRbPmrf4Eg== 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 v7 08/21] KVM: VMX: Save/restore guest FRED RSP0 Date: Fri, 29 Aug 2025 08:31:36 -0700 Message-ID: <20250829153149.2871901-9-xin@zytor.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20250829153149.2871901-1-xin@zytor.com> References: <20250829153149.2871901-1-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 | 13 +++++++++++++ arch/x86/kvm/vmx/vmx.h | 1 + 2 files changed, 14 insertions(+) diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 368f1799394c..5f639fb3b44d 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -1293,6 +1293,9 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcp= u) } =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 +1340,16 @@ 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 2.51.0