From: Jim Mattson <jmattson@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Joerg Roedel <joro@8bytes.org>, kvm list <kvm@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Yu Zhang <yu.c.zhang@linux.intel.com>,
Maxim Levitsky <mlevitsk@redhat.com>
Subject: Re: [PATCH 07/54] KVM: x86: Alert userspace that KVM_SET_CPUID{,2} after KVM_RUN is broken
Date: Wed, 23 Jun 2021 12:02:19 -0700 [thread overview]
Message-ID: <CALMp9eQG-QLm1xRXw2CxLEsRukH0q6HoaQKPraDo-TyCSv6EKg@mail.gmail.com> (raw)
In-Reply-To: <af716f56-9d68-2514-7b85-f9bbb1a82acf@redhat.com>
On Wed, Jun 23, 2021 at 11:49 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 23/06/21 20:11, Jim Mattson wrote:
> > On Wed, Jun 23, 2021 at 10:11 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
> >> Nah, that's not the philosophy. The philosophy is that covering all
> >> possible ways for userspace to shoot itself in the foot is impossible.
> >>
> >> However, here we're talking about 2 lines of code (thanks also to your
> >> patches that add last_vmentry_cpu for completely unrelated reasons) to
> >> remove a whole set of bullet/foot encounters.
> >
> > What about the problems that arise when we have different CPUID tables
> > for different vCPUs in the same VM? Can we just replace this
> > hole-in-foot inducing ioctl with a KVM_VM_SET_CPUID ioctl on the VM
> > level that has to be called before any vCPUs are created?
>
> Are there any KVM bugs that this can fix? The problem is that, unlike
> this case, it would be effectively impossible to deprecate
> KVM_SET_CPUID2 as a vcpu ioctl, so it would be hard to reap any benefits
> in KVM.
>
> BTW, there is actually a theoretical usecase for KVM_SET_CPUID2 after
> KVM_RUN, which is to test OSes against microcode updates that hide,
> totally random example, the RTM bit. But it's still not worth keeping
> it given 1) the bugs and complications in KVM, 2) if you really wanted
> that kind of testing so hard, the fact that you can just create a new
> vcpu file descriptor from scratch, possibly in cooperation with
> userspace MSR filtering 3) AFAIK no one has done that anyway in 15 years.
Though such a usecase may exist, I don't think it actually works
today. For example, kvm_vcpu_after_set_cpuid() potentially changes the
value of the guest IA32_PERF_GLOBAL_CTRL MSR.
next prev parent reply other threads:[~2021-06-23 19:02 UTC|newest]
Thread overview: 103+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-22 17:56 [PATCH 00/54] KVM: x86/mmu: Bug fixes and summer cleaning Sean Christopherson
2021-06-22 17:56 ` [PATCH 01/54] KVM: x86/mmu: Remove broken WARN that fires on 32-bit KVM w/ nested EPT Sean Christopherson
2021-06-22 17:56 ` [PATCH 02/54] KVM: x86/mmu: Treat NX as used (not reserved) for all !TDP shadow MMUs Sean Christopherson
2021-06-22 17:56 ` [PATCH 03/54] KVM: x86: Properly reset MMU context at vCPU RESET/INIT Sean Christopherson
2021-06-23 13:59 ` Paolo Bonzini
2021-06-23 14:01 ` Paolo Bonzini
2021-06-23 14:50 ` Sean Christopherson
2021-06-22 17:56 ` [PATCH 04/54] KVM: x86/mmu: Use MMU's role to detect CR4.SMEP value in nested NPT walk Sean Christopherson
2021-06-22 17:56 ` [PATCH 05/54] Revert "KVM: x86/mmu: Drop kvm_mmu_extended_role.cr4_la57 hack" Sean Christopherson
2021-06-25 8:47 ` Yu Zhang
2021-06-25 8:57 ` Paolo Bonzini
2021-06-25 9:29 ` Yu Zhang
2021-06-25 10:25 ` Paolo Bonzini
2021-06-25 11:23 ` Yu Zhang
2021-06-22 17:56 ` [PATCH 06/54] KVM: x86: Force all MMUs to reinitialize if guest CPUID is modified Sean Christopherson
2021-06-22 17:56 ` [PATCH 07/54] KVM: x86: Alert userspace that KVM_SET_CPUID{,2} after KVM_RUN is broken Sean Christopherson
2021-06-23 14:16 ` Paolo Bonzini
2021-06-23 17:00 ` Jim Mattson
2021-06-23 17:11 ` Paolo Bonzini
2021-06-23 18:11 ` Jim Mattson
2021-06-23 18:49 ` Paolo Bonzini
2021-06-23 19:02 ` Jim Mattson [this message]
2021-06-23 19:53 ` Paolo Bonzini
2021-06-22 17:56 ` [PATCH 08/54] Revert "KVM: MMU: record maximum physical address width in kvm_mmu_extended_role" Sean Christopherson
2021-06-25 8:52 ` Yu Zhang
2021-06-22 17:56 ` [PATCH 09/54] KVM: x86/mmu: Unconditionally zap unsync SPs when creating >4k SP at GFN Sean Christopherson
2021-06-23 14:36 ` Paolo Bonzini
2021-06-23 15:08 ` Sean Christopherson
2021-06-23 16:38 ` Paolo Bonzini
2021-06-23 22:04 ` Sean Christopherson
2021-06-25 9:51 ` Yu Zhang
2021-06-25 10:26 ` Paolo Bonzini
2021-06-25 13:08 ` Yu Zhang
2021-06-22 17:56 ` [PATCH 10/54] KVM: x86/mmu: Replace EPT shadow page shenanigans with simpler check Sean Christopherson
2021-06-23 15:49 ` Paolo Bonzini
2021-06-23 16:17 ` Sean Christopherson
2021-06-23 16:41 ` Paolo Bonzini
2021-06-23 16:54 ` Sean Christopherson
2021-06-22 17:56 ` [PATCH 11/54] KVM: x86/mmu: WARN and zap SP when sync'ing if MMU role mismatches Sean Christopherson
2021-06-22 17:56 ` [PATCH 12/54] KVM: x86/mmu: Drop the intermediate "transient" __kvm_sync_page() Sean Christopherson
2021-06-23 16:54 ` Paolo Bonzini
2021-06-22 17:56 ` [PATCH 13/54] KVM: x86/mmu: Rename unsync helper and update related comments Sean Christopherson
2021-06-22 17:56 ` [PATCH 14/54] KVM: x86: Fix sizes used to pass around CR0, CR4, and EFER Sean Christopherson
2021-06-22 17:57 ` [PATCH 15/54] KVM: nSVM: Add a comment to document why nNPT uses vmcb01, not vCPU state Sean Christopherson
2021-06-23 17:06 ` Paolo Bonzini
2021-06-23 20:49 ` Sean Christopherson
2021-06-22 17:57 ` [PATCH 16/54] KVM: x86/mmu: Drop smep_andnot_wp check from "uses NX" for shadow MMUs Sean Christopherson
2021-06-23 17:11 ` Paolo Bonzini
2021-06-23 19:36 ` Sean Christopherson
2021-06-22 17:57 ` [PATCH 17/54] KVM: x86: Read and pass all CR0/CR4 role bits to shadow MMU helper Sean Christopherson
2021-06-22 17:57 ` [PATCH 18/54] KVM: x86/mmu: Move nested NPT reserved bit calculation into MMU proper Sean Christopherson
2021-06-23 17:13 ` Paolo Bonzini
2021-06-22 17:57 ` [PATCH 19/54] KVM: x86/mmu: Grab shadow root level from mmu_role for shadow MMUs Sean Christopherson
2021-06-22 17:57 ` [PATCH 20/54] KVM: x86/mmu: Add struct and helpers to retrieve MMU role bits from regs Sean Christopherson
2021-06-23 1:58 ` kernel test robot
2021-06-23 17:18 ` Paolo Bonzini
2021-06-22 17:57 ` [PATCH 21/54] KVM: x86/mmu: Consolidate misc updates into shadow_mmu_init_context() Sean Christopherson
2021-06-22 17:57 ` [PATCH 22/54] KVM: x86/mmu: Ignore CR0 and CR4 bits in nested EPT MMU role Sean Christopherson
2021-06-22 17:57 ` [PATCH 23/54] KVM: x86/mmu: Use MMU's role_regs, not vCPU state, to compute mmu_role Sean Christopherson
2021-06-22 17:57 ` [PATCH 24/54] KVM: x86/mmu: Rename "nxe" role bit to "efer_nx" for macro shenanigans Sean Christopherson
2021-06-22 17:57 ` [PATCH 25/54] KVM: x86/mmu: Add helpers to query mmu_role bits Sean Christopherson
2021-06-23 20:02 ` Paolo Bonzini
2021-06-23 20:47 ` Sean Christopherson
2021-06-23 20:53 ` Paolo Bonzini
2021-06-22 17:57 ` [PATCH 26/54] KVM: x86/mmu: Do not set paging-related bits in MMU role if CR0.PG=0 Sean Christopherson
2021-06-22 17:57 ` [PATCH 27/54] KVM: x86/mmu: Set CR4.PKE/LA57 in MMU role iff long mode is active Sean Christopherson
2021-06-22 17:57 ` [PATCH 28/54] KVM: x86/mmu: Always Set new mmu_role immediately after checking old role Sean Christopherson
2021-06-22 17:57 ` [PATCH 29/54] KVM: x86/mmu: Don't grab CR4.PSE for calculating shadow reserved bits Sean Christopherson
2021-06-22 17:57 ` [PATCH 30/54] KVM: x86/mmu: Use MMU's role to get CR4.PSE for computing rsvd bits Sean Christopherson
2021-06-22 17:57 ` [PATCH 31/54] KVM: x86/mmu: Drop vCPU param from reserved bits calculator Sean Christopherson
2021-06-22 17:57 ` [PATCH 32/54] KVM: x86/mmu: Use MMU's role to compute permission bitmask Sean Christopherson
2021-06-22 17:57 ` [PATCH 33/54] KVM: x86/mmu: Use MMU's role to compute PKRU bitmask Sean Christopherson
2021-06-22 17:57 ` [PATCH 34/54] KVM: x86/mmu: Use MMU's roles to compute last non-leaf level Sean Christopherson
2021-06-22 17:57 ` [PATCH 35/54] KVM: x86/mmu: Use MMU's role to detect EFER.NX in guest page walk Sean Christopherson
2021-06-22 17:57 ` [PATCH 36/54] KVM: x86/mmu: Use MMU's role/role_regs to compute context's metadata Sean Christopherson
2021-06-22 17:57 ` [PATCH 37/54] KVM: x86/mmu: Use MMU's role to get EFER.NX during MMU configuration Sean Christopherson
2021-06-22 17:57 ` [PATCH 38/54] KVM: x86/mmu: Drop "nx" from MMU context now that there are no readers Sean Christopherson
2021-06-22 17:57 ` [PATCH 39/54] KVM: x86/mmu: Get nested MMU's root level from the MMU's role Sean Christopherson
2021-06-22 17:57 ` [PATCH 40/54] KVM: x86/mmu: Use MMU role_regs to get LA57, and drop vCPU LA57 helper Sean Christopherson
2021-06-22 17:57 ` [PATCH 41/54] KVM: x86/mmu: Consolidate reset_rsvds_bits_mask() calls Sean Christopherson
2021-06-23 20:07 ` Paolo Bonzini
2021-06-23 20:53 ` Sean Christopherson
2021-06-22 17:57 ` [PATCH 42/54] KVM: x86/mmu: Don't update nested guest's paging bitmasks if CR0.PG=0 Sean Christopherson
2021-06-22 17:57 ` [PATCH 43/54] KVM: x86/mmu: Add helper to update paging metadata Sean Christopherson
2021-06-22 17:57 ` [PATCH 44/54] KVM: x86/mmu: Add a helper to calculate root from role_regs Sean Christopherson
2021-06-22 17:57 ` [PATCH 45/54] KVM: x86/mmu: Collapse 32-bit PAE and 64-bit statements for helpers Sean Christopherson
2021-06-22 17:57 ` [PATCH 46/54] KVM: x86/mmu: Use MMU's role to determine PTTYPE Sean Christopherson
2021-06-22 17:57 ` [PATCH 47/54] KVM: x86/mmu: Add helpers to do full reserved SPTE checks w/ generic MMU Sean Christopherson
2021-06-23 20:13 ` Paolo Bonzini
2021-06-22 17:57 ` [PATCH 48/54] KVM: x86/mmu: WARN on any reserved SPTE value when making a valid SPTE Sean Christopherson
2021-06-22 17:57 ` [PATCH 49/54] KVM: x86: Enhance comments for MMU roles and nested transition trickiness Sean Christopherson
2021-06-22 17:57 ` [PATCH 50/54] KVM: x86/mmu: Optimize and clean up so called "last nonleaf level" logic Sean Christopherson
2021-06-23 20:22 ` Paolo Bonzini
2021-06-23 20:58 ` Sean Christopherson
2021-06-22 17:57 ` [PATCH 51/54] KVM: x86/mmu: Drop redundant rsvd bits reset for nested NPT Sean Christopherson
2021-06-22 17:57 ` [PATCH 52/54] KVM: x86/mmu: Get CR0.WP from MMU, not vCPU, in shadow page fault Sean Christopherson
2021-06-22 17:57 ` [PATCH 53/54] KVM: x86/mmu: Get CR4.SMEP " Sean Christopherson
2021-06-22 17:57 ` [PATCH 54/54] KVM: x86/mmu: Let guest use GBPAGES if supported in hardware and TDP is on Sean Christopherson
2021-06-23 20:29 ` [PATCH 00/54] KVM: x86/mmu: Bug fixes and summer cleaning Paolo Bonzini
2021-06-23 21:06 ` Sean Christopherson
2021-06-23 21:33 ` Paolo Bonzini
2021-06-23 22:08 ` Sean Christopherson
2021-06-23 22:12 ` Paolo Bonzini
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