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From: "Tian, Kevin" <kevin.tian@intel.com>
To: "Christopherson,, Sean" <seanjc@google.com>,
	"Liu, Jing2" <jing2.liu@intel.com>
Cc: "x86@kernel.org" <x86@kernel.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
	"linux-kselftest@vger.kernel.org"
	<linux-kselftest@vger.kernel.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"mingo@redhat.com" <mingo@redhat.com>,
	"bp@alien8.de" <bp@alien8.de>,
	"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
	"pbonzini@redhat.com" <pbonzini@redhat.com>,
	"corbet@lwn.net" <corbet@lwn.net>,
	"shuah@kernel.org" <shuah@kernel.org>,
	"Nakajima, Jun" <jun.nakajima@intel.com>,
	"jing2.liu@linux.intel.com" <jing2.liu@linux.intel.com>,
	"Zeng, Guang" <guang.zeng@intel.com>,
	"Wang, Wei W" <wei.w.wang@intel.com>,
	"Zhong, Yang" <yang.zhong@intel.com>
Subject: RE: [PATCH v3 05/22] kvm: x86: Check permitted dynamic xfeatures at KVM_SET_CPUID2
Date: Wed, 29 Dec 2021 02:18:28 +0000	[thread overview]
Message-ID: <BN9PR11MB52762FBBB5E887385F8DCC038C449@BN9PR11MB5276.namprd11.prod.outlook.com> (raw)
In-Reply-To: <YcugDN+9d8t4r9bV@google.com>

> From: Sean Christopherson <seanjc@google.com>
> Sent: Wednesday, December 29, 2021 7:39 AM
> 
> On Wed, Dec 22, 2021, Jing Liu wrote:
> > Guest xstate permissions should be set by userspace VMM before vcpu
> > creation. Extend KVM_SET_CPUID2 to verify that every feature reported
> > in CPUID[0xD] has proper permission set.
> 
> Why?  Nothing in the changelog, code, or comments explains why KVM
> _needs_ to prevent
> userspace from advertising bogus features to the guest.  E.g. the virtual
> address
> width check exists because _KVM_ will do the wrong thing given a width
> other than 48
> or 57, and explicity says as much in a comment.

Advertising a known bogus feature due to lacking of permission does
no good compared to failing it early even before the guest is running. This
also avoids tons of complexity at run-time to deal with permission
violation (e.g. introducing new kvm exit reason if you tracked the v2
discussion).

But yes, we should add a clear comment here.

Thanks
Kevin

  reply	other threads:[~2021-12-29  2:18 UTC|newest]

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-22 12:40 [PATCH v3 00/22] AMX Support in KVM Jing Liu
2021-12-22 12:40 ` [PATCH v3 01/22] x86/fpu: Extend fpu_xstate_prctl() with guest permissions Jing Liu
2021-12-22 12:40 ` [PATCH v3 02/22] x86/fpu: Prepare guest FPU for dynamically enabled FPU features Jing Liu
2021-12-22 12:40 ` [PATCH v3 03/22] kvm: x86: Fix xstate_required_size() to follow XSTATE alignment rule Jing Liu
2021-12-22 12:40 ` [PATCH v3 04/22] kvm: x86: Exclude unpermitted xfeatures at KVM_GET_SUPPORTED_CPUID Jing Liu
2021-12-22 12:40 ` [PATCH v3 05/22] kvm: x86: Check permitted dynamic xfeatures at KVM_SET_CPUID2 Jing Liu
2021-12-28 23:38   ` Sean Christopherson
2021-12-29  2:18     ` Tian, Kevin [this message]
2021-12-22 12:40 ` [PATCH v3 06/22] x86/fpu: Make XFD initialization in __fpstate_reset() a function argument Jing Liu
2021-12-22 12:40 ` [PATCH v3 07/22] x86/fpu: Add guest support to xfd_enable_feature() Jing Liu
2021-12-22 12:40 ` [PATCH v3 08/22] x86/fpu: Provide fpu_update_guest_perm_features() for guest Jing Liu
2021-12-22 12:40 ` [PATCH v3 09/22] kvm: x86: Enable dynamic XSAVE features at KVM_SET_CPUID2 Jing Liu
2021-12-28 23:54   ` Sean Christopherson
2021-12-29  2:23     ` Tian, Kevin
2021-12-22 12:40 ` [PATCH v3 10/22] x86/fpu: Provide fpu_update_guest_xfd() for IA32_XFD emulation Jing Liu
2021-12-22 12:40 ` [PATCH v3 11/22] kvm: x86: Add emulation for IA32_XFD Jing Liu
2021-12-22 12:40 ` [PATCH v3 12/22] x86/fpu: Prepare xfd_err in struct fpu_guest Jing Liu
2021-12-22 12:40 ` [PATCH v3 13/22] kvm: x86: Intercept #NM for saving IA32_XFD_ERR Jing Liu
2021-12-29  0:09   ` Sean Christopherson
2021-12-29  2:52     ` Tian, Kevin
2021-12-29 17:37       ` Sean Christopherson
2021-12-29  6:50     ` Tian, Kevin
2021-12-29  8:13     ` Tian, Kevin
2021-12-22 12:40 ` [PATCH v3 14/22] kvm: x86: Emulate IA32_XFD_ERR for guest Jing Liu
2021-12-22 12:40 ` [PATCH v3 15/22] kvm: x86: Disable RDMSR interception of IA32_XFD_ERR Jing Liu
2021-12-22 12:40 ` [PATCH v3 16/22] kvm: x86: Add XCR0 support for Intel AMX Jing Liu
2021-12-29  0:21   ` Sean Christopherson
2021-12-29  3:01     ` Tian, Kevin
2021-12-22 12:40 ` [PATCH v3 17/22] kvm: x86: Add CPUID " Jing Liu
2021-12-22 12:40 ` [PATCH v3 18/22] x86/fpu: Add uabi_size to guest_fpu Jing Liu
2021-12-22 12:40 ` [PATCH v3 19/22] kvm: x86: Get/set expanded xstate buffer Jing Liu
2021-12-29  0:38   ` Sean Christopherson
2021-12-29  2:57     ` Wang, Wei W
2021-12-29  6:36       ` Tian, Kevin
2021-12-22 12:40 ` [PATCH v3 20/22] kvm: selftests: Add support for KVM_CAP_XSAVE2 Jing Liu
2021-12-22 12:40 ` [PATCH v3 21/22] x86/fpu: Provide fpu_sync_guest_vmexit_xfd_state() Jing Liu
2021-12-22 12:40 ` [PATCH v3 22/22] kvm: x86: Disable interception for IA32_XFD on demand Jing Liu
2021-12-29  1:04   ` Sean Christopherson
2021-12-29  3:35     ` Tian, Kevin
2021-12-29  7:16     ` Tian, Kevin
2021-12-29 17:26       ` Sean Christopherson
2021-12-30  1:28         ` Tian, Kevin
2021-12-30  7:04         ` Tian, Kevin
2021-12-31  9:42         ` Tian, Kevin
2021-12-29  7:37     ` Tian, Kevin
2022-01-04 18:32     ` Paolo Bonzini
2022-01-04 18:58       ` Sean Christopherson

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