From: "Tian, Kevin" <kevin.tian@intel.com>
To: "Wang, Wei W" <wei.w.wang@intel.com>, "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>,
"Zhong, Yang" <yang.zhong@intel.com>
Subject: RE: [PATCH v3 19/22] kvm: x86: Get/set expanded xstate buffer
Date: Wed, 29 Dec 2021 06:36:43 +0000 [thread overview]
Message-ID: <BN9PR11MB5276411D19957E7EA51C53A98C449@BN9PR11MB5276.namprd11.prod.outlook.com> (raw)
In-Reply-To: <96d1266eeeb8434f9e23f9a051e252e6@intel.com>
> From: Wang, Wei W <wei.w.wang@intel.com>
> Sent: Wednesday, December 29, 2021 10:58 AM
>
> > > Reuse KVM_SET_XSAVE for both old/new formats by reimplementing it to
> > > do properly-sized memdup_user() based on the guest fpu container.
> >
> > I'm confused, the first sentence says KVM_SET_XSAVE isn't suitable, the
> > second says it can be reused with minimal effort.
>
> Probably "doesn't support" sounds better than "isn't suitable" above. But
> plan to reword a bit:
>
> With KVM_CAP_XSAVE, userspace uses a hardcoded 4KB buffer to get/set
> xstate data from/to
> KVM. This doesn't work when dynamic features (e.g. AMX) are used by the
> guest, as KVM uses
> a full expanded xstate buffer for the guest fpu emulation, which is larger
> than 4KB.
>
> Add KVM_CAP_XSAVE2, and userspace gets the required xstate buffer size
> from KVM via
> KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2). KVM_SET_XSAVE is extended
> with the support to
> work with larger xstate data size passed from userspace. KVM_GET_XSAVE2
> is preferred to
> extending KVM_GET_XSAVE to work with large buffer size for backward-
> compatible considerations.
> (Link: https://lkml.org/lkml/2021/12/15/510)
>
> Also, update the api doc with the new KVM_GET_XSAVE2 ioctl.
>
Revised to:
--
With KVM_CAP_XSAVE, userspace uses a hardcoded 4KB buffer to get/set
xstate data from/to KVM. This doesn't work when dynamic xfeatures
(e.g. AMX) are exposed to the guest as they require a larger buffer
size.
Introduce a new capability (KVM_CAP_XSAVE2). Userspace VMM gets the
required xstate buffer size via KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2).
KVM_SET_XSAVE is extended to work with both legacy and new capabilities
by doing properly-sized memdup_user() based on the guest fpu container.
KVM_GET_XSAVE is kept for backward-compatible reason. Instead,
KVM_GET_XSAVE2 is introduced under KVM_CAP_XSAVE2 as the preferred
interface for getting xstate buffer (4KB or larger size) from KVM.
(Link: https://lkml.org/lkml/2021/12/15/510)
Also, update the api doc with the new KVM_GET_XSAVE2 ioctl
--
Thanks
Kevin
next prev parent reply other threads:[~2021-12-29 6:37 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
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 [this message]
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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