From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f200.google.com (mail-pf1-f200.google.com [209.85.210.200]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 18E223B19B3 for ; Thu, 27 Aug 2026 17:17:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.200 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787851062; cv=none; b=OYiK0XtinN1sjEE5bMTMNJEatIDIHphLI0czn6M/fIZqxf2bz/TtRYKOvxHT9QiYu34+WxRa2NcfodzgugArCAsuFQHlCMg/QKLc8N5cxsr7C+cSbYDwZU0/PcfIru7w6KAWFoNbmYubKmqr7hh9krwI9+PKoBA12eipegdcX0M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787851062; c=relaxed/simple; bh=kZUvGMgDkJF0I421Gwxeg/moWCtG0J7dkmuLCb7CDHk=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=UhoeEHpejT6LHsn2paad2uRKOvht4qL7NddWoekA7SKQoxBoEh2yRKkIE5LVYEo1vafNU9KGMZZIO63hkHWxmbD4SW3x+ENWxuGbR2GQiOobF8HpoMS6bLiU+V692y0KPqm0oP0qIXSXuS4U55ndHZaHkmOVWOJ1yW3gB9jLJtM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=keFn2ScY; arc=none smtp.client-ip=209.85.210.200 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="keFn2ScY" Received: by mail-pf1-f200.google.com with SMTP id d2e1a72fcca58-85599cf98e5so296037b3a.1 for ; Thu, 27 Aug 2026 10:17:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1787851059; x=1788455859; darn=vger.kernel.org; h=content-transfer-encoding:content-type:cc:to:from:subject :message-id:references:mime-version:in-reply-to:date:from:to:cc :subject:date:message-id:reply-to:content-type; bh=aYBNRrzJEAv0A994/6qhRFOUK5yMN/F89xH3xrz0hxE=; b=keFn2ScYp+CFLLWVQwIJ61MXg0xQYNLGd0pEvM7SVZU20KAGSIVW5UAJetlwPLoW3b 4mG2np+N2SuU7+N2niCNngT7wS5hHAJOP/sdZz5qvQH1zSRVc9+4EQ/BSKbdT3uNmXrg QlbpMphGdv4Dus91r7IIy1Yi2TL4oDN9LXeYdTc1UK3/qnhtK4MpCAmi02l/W5NaE19O xQT5fsMnjMX/E6dcB/4p4WnN6z3zTEqVvCGJadQmOylV39xOsSP7jm0HqToel7wcHVbj O2WtBEwm9w3XXw45GYS9FgNRvnEYckwdtO56R0Ub+UtqIhmoO7+gB7RLoJ2waJAoUNPQ 4+1w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1787851059; x=1788455859; h=content-transfer-encoding:content-type:cc:to:from:subject :message-id:references:mime-version:in-reply-to:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=aYBNRrzJEAv0A994/6qhRFOUK5yMN/F89xH3xrz0hxE=; b=Li7HCrC8DQ2rCkouMLSwOLTqhK5jxOuyJsPjxO+n3deelsCpsXvETXtCPm350chiOi YOkEdB/hT5NYcwAz2jbJhQAS7RTe75oXo41h1EfJ2IQZCGlsFqmmpcLxK9ycUJLJiVl7 0KtMKWHn0+ovuJqFPd6h8mgSFUJ8n+ffgl7nfjYmWgDKmAomCKECF59PvhuRswLBIxBU n5qOuqWM3M4bIDO+z/9otS1AnjeoLK5x1m6LsouU1Vv1UeCrJ5mj7AZdFXXBqRf6yQD/ NHrhlVc4GLkb8y23S9cVztizYStBC1zPPlRaAdH5Mes8Vd8DGJhG//HF0ZXYg6X09EEv nJnw== X-Forwarded-Encrypted: i=1; AHgh+RryPmE1ReKM0iXsRAzHQSOFAPcI/59bbXusVuXuiHC/nd8/rYAb1DDIoCwyBmMAJGSukZg=@vger.kernel.org X-Gm-Message-State: AFuF++krjJRvG6q0CMvyPoCWd+3NByug2p11rVZ84MRWmHYRdh3SRMeF Z3VgiA8QOg3OLv9Pn97NbPQbjQXl17E1skNoC5BoIV2//Lrhi+Vrc0FIq8B9AsFhyZSKuR6wEOw 84QIePw== X-Received: from pfbhg6.prod.google.com ([2002:a05:6a00:8606:b0:848:3f4b:c4da]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:2da7:b0:851:bf92:34c9 with SMTP id d2e1a72fcca58-8562a8d2cdfmr1241692b3a.9.1787851059240; Thu, 27 Aug 2026 10:17:39 -0700 (PDT) Date: Thu, 27 Aug 2026 10:17:38 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260826233919.998904-1-seanjc@google.com> <20260826233919.998904-13-seanjc@google.com> Message-ID: Subject: Re: [PATCH v3 12/13] KVM: selftests: Dedup assembly code for VMLAUNCH and VMRESUME From: Sean Christopherson To: Yosry Ahmed Cc: Paolo Bonzini , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, f734222792@gmail.com, Vitaly Kuznetsov , Sashiko Bot Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Thu, Aug 27, 2026, Yosry Ahmed wrote: > On Thu, Aug 27, 2026 at 9:41=E2=80=AFAM Sean Christopherson wrote: > > #define __BUILD_VMX_VM_ENTRY_HELPER(insn, prefix, vmwrite_insn, vmwri= te_operand, \ > > __host_rsp, __host_rip) = \ >=20 > The only part I really hate is vmwrite_operand. Why do we need it? Seems > like all the current helpers use "r", I feel like I am missing something. ... > > static int __##prefix##_##insn(void) = \ > > { = \ > > int ret; = \ > > = \ > > __asm__ __volatile__("push $0;" = \ > > __stringify(vmwrite_insn) " %%rsp, %[host_= rsp];" \ > > "lea 1f(%%rip), %%rax;" = \ > > __stringify(vmwrite_insn) " %%rax, %[host_= rip];" \ > > VMX_SWITCH_GPRS_ASM = \ > > __stringify(insn)";" = \ > > "incq (%%rsp);" = \ > > "1: ;" = \ > > VMX_SWITCH_GPRS_ASM = \ > > "pop %%rax;" = \ > > : [ret]"=3D&a"(ret) = \ > > : [host_rsp]__stringify(vmwrite_operand)(_= _host_rsp), \ > > [host_rip]__stringify(vmwrite_operand)(_= _host_rip), \ > > GUEST_REGS_OFFSETS = \ > > : "memory", "cc"); = \ > > return ret; = \ > > } > > > > #define BUILD_VMX_VM_ENTRY_HELPER(insn) \ > > __BUILD_VMX_VM_ENTRY_HELPER(insn, _, vmwrite, r, (u64)HOST_RSP,= (u64)HOST_RIP) \ > > __BUILD_VMX_VM_ENTRY_HELPER(insn, __evmcs, mov, m, = \ > > current_evmcs->host_rsp, current_ev= mcs->host_rip) eVMCS is a memory operand, i.e. it's MOV RSP, [evmcs->host_rip]. The exist= ing evmcs_{vmresume,vmlaunch}() code is rather stupid and loads the address int= o a register, and then manually encodes MOV RSP, []. P.S. just in case you didn't already think this code is evil, the '&' in th= e above "[ret]"=3D&a"(ret)" is an earlyclobber that tells the compiler t= hat RAX may be clobbered before all inputs and processed, i.e. prevents th= e compiler from using RAX for VMWRITE's register operand, or from using = RAX to compute the memory operand for eVMCS's MOV. P.P.S. even though the prototype for VMWRITE is "VMWRITE r64, r/m64", Intel= is ass-backwards when it comes to syntax, i.e r/m64 is the source, not = the dest, and so the field encoding *must* be a register operand. I.e. = we can't do something like this: diff --git tools/testing/selftests/kvm/lib/x86/vmx.c tools/testing/selftest= s/kvm/lib/x86/vmx.c index 1a8515de42b0..b5efd10950c7 100644 --- tools/testing/selftests/kvm/lib/x86/vmx.c +++ tools/testing/selftests/kvm/lib/x86/vmx.c @@ -179,7 +179,10 @@ void load_vmcs(struct vmx_pages *vmx) vmclear(vmx->shadow_vmcs_gpa); } =20 -#define __BUILD_VMX_VM_ENTRY_HELPER(insn, prefix, vmwrite_insn, vmwrite_op= erand, \ +const u64 HOST_RSP_ENCODING =3D HOST_RSP; +const u64 HOST_RIP_ENCODING =3D HOST_RIP; + +#define __BUILD_VMX_VM_ENTRY_HELPER(insn, prefix, vmwrite_insn, \ __host_rsp, __host_rip) = \ static int __##prefix##_##insn(void) = \ { = \ @@ -196,16 +199,17 @@ static int __##prefix##_##insn(void) = \ VMX_SWITCH_GPRS_ASM = \ "pop %%rax;" = \ : [ret]"=3D&a"(ret) = \ - : [host_rsp]__stringify(vmwrite_operand)(__hos= t_rsp), \ - [host_rip]__stringify(vmwrite_operand)(__hos= t_rip), \ + : [host_rsp]"m"(__host_rsp), = \ + [host_rip]"m"(__host_rip), = \ GUEST_REGS_OFFSETS = \ : "memory", "cc"); = \ return ret; = \ } =20 #define BUILD_VMX_VM_ENTRY_HELPER(insn) \ - __BUILD_VMX_VM_ENTRY_HELPER(insn, _, vmwrite, r, (u64)HOST_RSP, (u6= 4)HOST_RIP) \ - __BUILD_VMX_VM_ENTRY_HELPER(insn, __evmcs, mov, m, = \ + __BUILD_VMX_VM_ENTRY_HELPER(insn, _, vmwrite, = \ + HOST_RSP_ENCODING, HOST_RIP_ENCODING) = \ + __BUILD_VMX_VM_ENTRY_HELPER(insn, __evmcs, mov, = \ current_evmcs->host_rsp, current_evmcs-= >host_rip) =20 BUILD_VMX_VM_ENTRY_HELPER(vmlaunch)