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d="scan'208";a="78644900" From: Andrew Cooper To: Xen-devel CC: Andrew Cooper , Jan Beulich , =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= , Wei Liu Subject: [PATCH 3/3] x86/spec-ctrl: Shrink further entry paths due to %rdx being 0 Date: Mon, 18 Jul 2022 21:50:09 +0100 Message-ID: <20220718205009.3557-4-andrew.cooper3@citrix.com> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20220718205009.3557-1-andrew.cooper3@citrix.com> References: <20220718205009.3557-1-andrew.cooper3@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-ZohoMail-DKIM: pass (identity @citrix.com) X-ZM-MESSAGEID: 1658177470417100001 This is a continuation of the observation from: e9b8d31981f1 ("x86/spec-ctrl: Rework SPEC_CTRL_ENTRY_FROM_INTR_IST") 53a570b28569 ("x86/spec-ctrl: Support IBPB-on-entry") With %rdx known to be zero and not clobbered on the early entry path, we do= n't need to re-zero it every time want to write to an MSR. Signed-off-by: Andrew Cooper Reviewed-by: Jan Beulich --- CC: Jan Beulich CC: Roger Pau Monn=C3=A9 CC: Wei Liu --- xen/arch/x86/hvm/vmx/entry.S | 4 +--- xen/arch/x86/include/asm/spec_ctrl_asm.h | 3 +-- 2 files changed, 2 insertions(+), 5 deletions(-) diff --git a/xen/arch/x86/hvm/vmx/entry.S b/xen/arch/x86/hvm/vmx/entry.S index 5f5de45a1309..392aca42b864 100644 --- a/xen/arch/x86/hvm/vmx/entry.S +++ b/xen/arch/x86/hvm/vmx/entry.S @@ -33,13 +33,12 @@ ENTRY(vmx_asm_vmexit_handler) movb $1,VCPU_vmx_launched(%rbx) mov %rax,VCPU_hvm_guest_cr2(%rbx) =20 - /* SPEC_CTRL_ENTRY_FROM_VMX Req: b=3Dcurr %rsp=3Dregs/cpuinfo, = Clob: acd */ + /* SPEC_CTRL_ENTRY_FROM_VMX Req: %rsp=3Dregs/cpuinfo, %rdx=3D0,= Clob: acd */ ALTERNATIVE "", DO_OVERWRITE_RSB, X86_FEATURE_SC_RSB_HVM =20 .macro restore_spec_ctrl mov $MSR_SPEC_CTRL, %ecx movzbl CPUINFO_xen_spec_ctrl(%rsp), %eax - xor %edx, %edx wrmsr .endm ALTERNATIVE "", restore_spec_ctrl, X86_FEATURE_SC_MSR_HVM @@ -49,7 +48,6 @@ ENTRY(vmx_asm_vmexit_handler) .macro restore_lbr mov $IA32_DEBUGCTLMSR_LBR, %eax mov $MSR_IA32_DEBUGCTLMSR, %ecx - xor %edx, %edx wrmsr .endm ALTERNATIVE "", restore_lbr, X86_FEATURE_XEN_LBR diff --git a/xen/arch/x86/include/asm/spec_ctrl_asm.h b/xen/arch/x86/includ= e/asm/spec_ctrl_asm.h index fab27ff5532b..61eed8510ba9 100644 --- a/xen/arch/x86/include/asm/spec_ctrl_asm.h +++ b/xen/arch/x86/include/asm/spec_ctrl_asm.h @@ -176,7 +176,7 @@ .macro DO_SPEC_CTRL_ENTRY maybexen:req /* * Requires %rsp=3Dregs (also cpuinfo if !maybexen) - * Requires %r14=3Dstack_end (if maybexen) + * Requires %r14=3Dstack_end (if maybexen), %rdx=3D0 * Clobbers %rax, %rcx, %rdx * * PV guests can't update MSR_SPEC_CTRL behind Xen's back, so no need to r= ead @@ -184,7 +184,6 @@ * while entries from Xen must leave shadowing in its current state. */ mov $MSR_SPEC_CTRL, %ecx - xor %edx, %edx =20 /* * Clear SPEC_CTRL shadowing *before* loading Xen's value. If entering --=20 2.11.0