From: Peter Zijlstra <peterz@infradead.org>
To: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Sean Christopherson <seanjc@google.com>,
Weijiang Yang <weijiang.yang@intel.com>,
pbonzini@redhat.com, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, rppt@kernel.org,
binbin.wu@linux.intel.com, rick.p.edgecombe@intel.com,
john.allen@amd.com, Chao Gao <chao.gao@intel.com>,
Andrew Cooper <Andrew.Cooper3@citrix.com>
Subject: Re: [PATCH v3 00/21] Enable CET Virtualization
Date: Thu, 20 Jul 2023 10:09:47 +0200 [thread overview]
Message-ID: <20230720080947.GA3570477@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20230720080357.GA3569127@hirez.programming.kicks-ass.net>
On Thu, Jul 20, 2023 at 10:03:58AM +0200, Peter Zijlstra wrote:
> > Trying to understand more what prevents SSS to enable in pre FRED, Is
> > it better #CP exception
> > handling with other nested exceptions?
>
> SSS took the syscall gap and made it worse -- as in *way* worse.
>
> To top it off, the whole SSS busy bit thing is fundamentally
> incompatible with how we manage to survive nested exceptions in NMI
> context.
>
> Basically, the whole x86 exception / stack switching logic was already
> borderline impossible (consider taking an MCE in the early NMI path
> where we set up, but have not finished, the re-entrancy stuff), and
SSS
> pushed it over the edge and set it on fire.
>
> And NMI isn't the only problem, the various new virt exceptions #VC and
> #HV are on their own already near impossible, adding SSS again pushes
> the whole thing into clear insanity.
>
> There's a good exposition of the whole trainwreck by Andrew here:
>
> https://www.youtube.com/watch?v=qcORS8CN0ow
>
> (that is, sorry for the youtube link, but Google is failing me in
> finding the actual Google Doc that talk is based on, or even the slide
> deck :/)
>
>
>
> FRED solves all that by:
>
> - removing the stack gap, cc/ip/ss/sp/ssp/gs will all be switched
> atomically and consistently for every transition.
>
> - removing the non-reentrant IST mechanism and replacing it with stack
> levels
>
> - adding an explicit NMI latch
>
> - re-organising the actual shadow stacks and doing away with that busy
> bit thing (I need to re-read the FRED spec on this detail again).
>
>
>
> Crazy as we are, we're not touching legacy/IDT SSS with a ten foot pole,
> sorry.
next prev parent reply other threads:[~2023-07-20 8:10 UTC|newest]
Thread overview: 99+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-11 4:08 Yang Weijiang
2023-05-11 4:08 ` [PATCH v3 01/21] x86/shstk: Add Kconfig option for shadow stack Yang Weijiang
2023-05-11 4:08 ` [PATCH v3 02/21] x86/cpufeatures: Add CPU feature flags for shadow stacks Yang Weijiang
2023-05-11 4:08 ` [PATCH v3 03/21] x86/cpufeatures: Enable CET CR4 bit for shadow stack Yang Weijiang
2023-05-11 4:08 ` [PATCH v3 04/21] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states Yang Weijiang
2023-05-11 4:08 ` [PATCH v3 05/21] x86/fpu: Add helper for modifying xstate Yang Weijiang
2023-05-11 4:08 ` [PATCH v3 06/21] KVM:x86: Report XSS as to-be-saved if there are supported features Yang Weijiang
2023-05-24 7:06 ` Chao Gao
2023-05-24 8:19 ` Yang, Weijiang
2023-05-11 4:08 ` [PATCH v3 07/21] KVM:x86: Refresh CPUID on write to guest MSR_IA32_XSS Yang Weijiang
2023-05-25 6:10 ` Chao Gao
2023-05-30 3:51 ` Yang, Weijiang
2023-05-30 12:08 ` Chao Gao
2023-05-31 1:11 ` Yang, Weijiang
2023-06-15 23:45 ` Sean Christopherson
2023-06-16 1:58 ` Yang, Weijiang
2023-06-23 23:21 ` Sean Christopherson
2023-06-26 9:24 ` Yang, Weijiang
2023-05-11 4:08 ` [PATCH v3 08/21] KVM:x86: Init kvm_caps.supported_xss with supported feature bits Yang Weijiang
2023-06-06 8:38 ` Chao Gao
2023-06-08 5:42 ` Yang, Weijiang
2023-05-11 4:08 ` [PATCH v3 09/21] KVM:x86: Load guest FPU state when accessing xsaves-managed MSRs Yang Weijiang
2023-06-15 23:50 ` Sean Christopherson
2023-06-16 2:02 ` Yang, Weijiang
2023-05-11 4:08 ` [PATCH v3 10/21] KVM:x86: Add #CP support in guest exception classification Yang Weijiang
2023-06-06 9:08 ` Chao Gao
2023-06-08 6:01 ` Yang, Weijiang
2023-06-15 23:58 ` Sean Christopherson
2023-06-16 6:56 ` Yang, Weijiang
2023-06-16 18:57 ` Sean Christopherson
2023-06-19 9:28 ` Yang, Weijiang
2023-06-30 9:34 ` Yang, Weijiang
2023-06-30 10:27 ` Chao Gao
2023-06-30 12:05 ` Yang, Weijiang
2023-06-30 15:05 ` Neiger, Gil
2023-06-30 15:15 ` Sean Christopherson
2023-07-01 1:58 ` Yang, Weijiang
2023-07-01 1:54 ` Yang, Weijiang
2023-06-30 15:07 ` Sean Christopherson
2023-06-30 15:21 ` Neiger, Gil
2023-07-01 1:57 ` Yang, Weijiang
2023-05-11 4:08 ` [PATCH v3 11/21] KVM:VMX: Introduce CET VMCS fields and control bits Yang Weijiang
2023-05-11 4:08 ` [PATCH v3 12/21] KVM:x86: Add fault checks for guest CR4.CET setting Yang Weijiang
2023-06-06 11:03 ` Chao Gao
2023-06-08 6:06 ` Yang, Weijiang
2023-05-11 4:08 ` [PATCH v3 13/21] KVM:VMX: Emulate reads and writes to CET MSRs Yang Weijiang
2023-05-23 8:21 ` Binbin Wu
2023-05-24 2:49 ` Yang, Weijiang
2023-06-23 23:53 ` Sean Christopherson
2023-06-26 14:05 ` Yang, Weijiang
2023-06-26 21:15 ` Sean Christopherson
2023-06-27 3:32 ` Yang, Weijiang
2023-06-27 14:55 ` Sean Christopherson
2023-06-28 1:42 ` Yang, Weijiang
2023-07-07 9:10 ` Yang, Weijiang
2023-07-07 15:28 ` Neiger, Gil
2023-07-12 16:42 ` Sean Christopherson
2023-05-11 4:08 ` [PATCH v3 14/21] KVM:VMX: Add a synthetic MSR to allow userspace to access GUEST_SSP Yang Weijiang
2023-05-23 8:57 ` Binbin Wu
2023-05-24 2:55 ` Yang, Weijiang
2023-05-11 4:08 ` [PATCH v3 15/21] KVM:x86: Report CET MSRs as to-be-saved if CET is supported Yang Weijiang
2023-05-11 4:08 ` [PATCH v3 16/21] KVM:x86: Save/Restore GUEST_SSP to/from SMM state save area Yang Weijiang
2023-06-23 22:30 ` Sean Christopherson
2023-06-26 8:59 ` Yang, Weijiang
2023-06-26 21:20 ` Sean Christopherson
2023-06-27 3:50 ` Yang, Weijiang
2023-05-11 4:08 ` [PATCH v3 17/21] KVM:VMX: Pass through user CET MSRs to the guest Yang Weijiang
2023-05-11 4:08 ` [PATCH v3 18/21] KVM:x86: Enable CET virtualization for VMX and advertise to userspace Yang Weijiang
2023-05-24 6:35 ` Chenyi Qiang
2023-05-24 8:07 ` Yang, Weijiang
2023-05-11 4:08 ` [PATCH v3 19/21] KVM:nVMX: Enable user CET support for nested VMX Yang Weijiang
2023-05-11 4:08 ` [PATCH v3 20/21] KVM:x86: Enable kernel IBT support for guest Yang Weijiang
2023-06-24 0:03 ` Sean Christopherson
2023-06-26 12:10 ` Yang, Weijiang
2023-06-26 20:50 ` Sean Christopherson
2023-06-27 1:53 ` Yang, Weijiang
2023-05-11 4:08 ` [PATCH v3 21/21] KVM:x86: Support CET supervisor shadow stack MSR access Yang Weijiang
2023-06-15 23:30 ` [PATCH v3 00/21] Enable CET Virtualization Sean Christopherson
2023-06-16 0:00 ` Sean Christopherson
2023-06-16 1:00 ` Yang, Weijiang
2023-06-16 8:25 ` Yang, Weijiang
2023-06-16 17:56 ` Sean Christopherson
2023-06-19 6:41 ` Yang, Weijiang
2023-06-23 20:51 ` Sean Christopherson
2023-06-26 6:46 ` Yang, Weijiang
2023-07-17 7:44 ` Yang, Weijiang
2023-07-19 19:41 ` Sean Christopherson
2023-07-19 20:26 ` Sean Christopherson
2023-07-20 1:58 ` Yang, Weijiang
2023-07-19 20:36 ` Peter Zijlstra
2023-07-20 5:26 ` Pankaj Gupta
2023-07-20 8:03 ` Peter Zijlstra
2023-07-20 8:09 ` Peter Zijlstra [this message]
2023-07-20 9:14 ` Pankaj Gupta
2023-07-20 10:46 ` Andrew Cooper
2023-07-20 1:55 ` Yang, Weijiang
2023-07-10 0:28 ` Yang, Weijiang
2023-07-10 22:18 ` Sean Christopherson
2023-07-11 1:24 ` Yang, Weijiang
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