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Date: Tue, 8 Nov 2016 09:42:57 -0800
From: Kyle Huey <me@...ehuey.com>
To: David Matlack <dmatlack@...gle.com>
Cc: "Robert O'Callahan" <robert@...llahan.org>,
Thomas Gleixner <tglx@...utronix.de>,
Andy Lutomirski <luto@...nel.org>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Radim Krčmář <rkrcmar@...hat.com>,
Jeff Dike <jdike@...toit.com>,
Richard Weinberger <richard@....at>,
Alexander Viro <viro@...iv.linux.org.uk>,
Shuah Khan <shuah@...nel.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Borislav Petkov <bp@...e.de>,
Peter Zijlstra <peterz@...radead.org>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Len Brown <len.brown@...el.com>,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
Dmitry Safonov <dsafonov@...tuozzo.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"open list:USER-MODE LINUX (UML)"
<user-mode-linux-devel@...ts.sourceforge.net>,
"open list:USER-MODE LINUX (UML)"
<user-mode-linux-user@...ts.sourceforge.net>,
"open list:FILESYSTEMS (VFS and infrastructure)"
<linux-fsdevel@...r.kernel.org>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@...r.kernel.org>, kvm list <kvm@...r.kernel.org>
Subject: Re: [PATCH v9 7/7] KVM: x86: virtualize cpuid faulting
On Mon, Nov 7, 2016 at 12:13 PM, David Matlack <dmatlack@...gle.com> wrote:
> On Sun, Nov 6, 2016 at 12:57 PM, Kyle Huey <me@...ehuey.com> wrote:
>> Hardware support for faulting on the cpuid instruction is not required to
>> emulate it, because cpuid triggers a VM exit anyways. KVM handles the relevant
>> MSRs (MSR_PLATFORM_INFO and MSR_MISC_FEATURES_ENABLE) and upon a
>> cpuid-induced VM exit checks the cpuid faulting state and the CPL.
>> kvm_require_cpl is even kind enough to inject the GP fault for us.
>>
>> Signed-off-by: Kyle Huey <khuey@...ehuey.com>
>> ---
>> arch/x86/include/asm/kvm_host.h | 2 ++
>> arch/x86/kvm/cpuid.c | 3 +++
>> arch/x86/kvm/x86.c | 28 ++++++++++++++++++++++++++++
>> 3 files changed, 33 insertions(+)
>>
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index bdde807..5edef7b 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -592,16 +592,18 @@ struct kvm_vcpu_arch {
>> u64 pat;
>>
>> unsigned switch_db_regs;
>> unsigned long db[KVM_NR_DB_REGS];
>> unsigned long dr6;
>> unsigned long dr7;
>> unsigned long eff_db[KVM_NR_DB_REGS];
>> unsigned long guest_debug_dr7;
>> + bool cpuid_fault_supported;
>> + bool cpuid_fault;
>
> Suggest storing these in MSR form:
>
> u64 msr_platform_info;
> u64 msr_misc_features_enables;
>
> It will simplify the MSR get/set code, and make it easier to plumb
> support for new bits in these MSRs.
I'm inclined to do this for MSR_PLATFORM_INFO but not
MSR_MISC_FEATURES_ENABLES. The former actually has other bits, and
isn't used outside the msr handling code (yet, anyways).
MSR_MISC_FEATURES_ENABLES doesn't have any other bits (it's actually
not documented by Intel at all outside of that virtualization paper)
and after masking bits in cpuid.c or adding a helper function the
complexity would be a wash at best.
>>
>> u64 mcg_cap;
>> u64 mcg_status;
>> u64 mcg_ctl;
>> u64 mcg_ext_ctl;
>> u64 *mce_banks;
>>
>> /* Cache MMIO info */
>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>> index afa7bbb..ed8436a 100644
>> --- a/arch/x86/kvm/cpuid.c
>> +++ b/arch/x86/kvm/cpuid.c
>> @@ -862,16 +862,19 @@ void kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx, u32 *ecx, u32 *edx)
>> trace_kvm_cpuid(function, *eax, *ebx, *ecx, *edx);
>> }
>> EXPORT_SYMBOL_GPL(kvm_cpuid);
>>
>> void kvm_emulate_cpuid(struct kvm_vcpu *vcpu)
>> {
>> u32 function, eax, ebx, ecx, edx;
>>
>> + if (vcpu->arch.cpuid_fault && !kvm_require_cpl(vcpu, 0))
>> + return;
>> +
>> function = eax = kvm_register_read(vcpu, VCPU_REGS_RAX);
>> ecx = kvm_register_read(vcpu, VCPU_REGS_RCX);
>> kvm_cpuid(vcpu, &eax, &ebx, &ecx, &edx);
>> kvm_register_write(vcpu, VCPU_REGS_RAX, eax);
>> kvm_register_write(vcpu, VCPU_REGS_RBX, ebx);
>> kvm_register_write(vcpu, VCPU_REGS_RCX, ecx);
>> kvm_register_write(vcpu, VCPU_REGS_RDX, edx);
>> kvm_x86_ops->skip_emulated_instruction(vcpu);
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 3017de0..9cd6462 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -986,16 +986,18 @@ static u32 emulated_msrs[] = {
>>
>> MSR_IA32_TSC_ADJUST,
>> MSR_IA32_TSCDEADLINE,
>> MSR_IA32_MISC_ENABLE,
>> MSR_IA32_MCG_STATUS,
>> MSR_IA32_MCG_CTL,
>> MSR_IA32_MCG_EXT_CTL,
>> MSR_IA32_SMBASE,
>> + MSR_PLATFORM_INFO,
>> + MSR_MISC_FEATURES_ENABLES,
>> };
>>
>> static unsigned num_emulated_msrs;
>>
>> bool kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer)
>> {
>> if (efer & efer_reserved_bits)
>> return false;
>> @@ -2269,16 +2271,29 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>> return 1;
>> vcpu->arch.osvw.length = data;
>> break;
>> case MSR_AMD64_OSVW_STATUS:
>> if (!guest_cpuid_has_osvw(vcpu))
>> return 1;
>> vcpu->arch.osvw.status = data;
>> break;
>> + case MSR_PLATFORM_INFO:
>> + if (!msr_info->host_initiated ||
>> + data & ~PLATINFO_CPUID_FAULT ||
>> + (!!(data & PLATINFO_CPUID_FAULT) && vcpu->arch.cpuid_fault))
>
> Should that be a single exclamation point?
Ah, yes, good catch.
>> + return 1;
>> + vcpu->arch.cpuid_fault_supported = !!(data & PLATINFO_CPUID_FAULT);
>
> No need for "!!".
>
>> + break;
>> + case MSR_MISC_FEATURES_ENABLES:
>> + if (data & ~CPUID_FAULT_ENABLE ||
>> + !vcpu->arch.cpuid_fault_supported)
>> + return 1;
>> + vcpu->arch.cpuid_fault = !!(data & CPUID_FAULT_ENABLE);
>
> No need for "!!".
Ok, but most (if not all) other assignments of bitmasking operations
to booleans use !! or explicit comparisons with zero in this file.
>> + break;
>> default:
>> if (msr && (msr == vcpu->kvm->arch.xen_hvm_config.msr))
>> return xen_hvm_config(vcpu, data);
>> if (kvm_pmu_is_valid_msr(vcpu, msr))
>> return kvm_pmu_set_msr(vcpu, msr_info);
>> if (!ignore_msrs) {
>> vcpu_unimpl(vcpu, "unhandled wrmsr: 0x%x data 0x%llx\n",
>> msr, data);
>> @@ -2483,16 +2498,26 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>> return 1;
>> msr_info->data = vcpu->arch.osvw.length;
>> break;
>> case MSR_AMD64_OSVW_STATUS:
>> if (!guest_cpuid_has_osvw(vcpu))
>> return 1;
>> msr_info->data = vcpu->arch.osvw.status;
>> break;
>> + case MSR_PLATFORM_INFO:
>> + msr_info->data = 0;
>> + if (vcpu->arch.cpuid_fault_supported)
>> + msr_info->data |= PLATINFO_CPUID_FAULT;
>> + break;
>> + case MSR_MISC_FEATURES_ENABLES:
>> + msr_info->data = 0;
>> + if (vcpu->arch.cpuid_fault)
>> + msr_info->data |= CPUID_FAULT_ENABLE;
>> + break;
>> default:
>> if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
>> return kvm_pmu_get_msr(vcpu, msr_info->index, &msr_info->data);
>> if (!ignore_msrs) {
>> vcpu_unimpl(vcpu, "unhandled rdmsr: 0x%x\n", msr_info->index);
>> return 1;
>> } else {
>> vcpu_unimpl(vcpu, "ignored rdmsr: 0x%x\n", msr_info->index);
>> @@ -7508,16 +7533,19 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>>
>> kvm_clear_async_pf_completion_queue(vcpu);
>> kvm_async_pf_hash_reset(vcpu);
>> vcpu->arch.apf.halted = false;
>>
>> if (!init_event) {
>> kvm_pmu_reset(vcpu);
>> vcpu->arch.smbase = 0x30000;
>> +
>> + vcpu->arch.cpuid_fault_supported = true;
>> + vcpu->arch.cpuid_fault = false;
>> }
>>
>> memset(vcpu->arch.regs, 0, sizeof(vcpu->arch.regs));
>> vcpu->arch.regs_avail = ~0;
>> vcpu->arch.regs_dirty = ~0;
>>
>> kvm_x86_ops->vcpu_reset(vcpu, init_event);
>> }
>> --
>> 2.10.2
>>
- Kyle
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