linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Jim Mattson <jmattson@google.com>
To: stsp <stsp2@yandex.ru>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <sean.j.christopherson@intel.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>
Subject: Re: KVM_SET_CPUID doesn't check supported bits (was Re: [PATCH 0/6] KVM: x86: KVM_SET_SREGS.CR4 bug fixes and cleanup)
Date: Mon, 7 Dec 2020 15:59:19 -0800	[thread overview]
Message-ID: <CALMp9eSMt1DwXL=wE-xyHcOyCvZzzHdgZ=N9Pqdm1CW6aSzOKw@mail.gmail.com> (raw)
In-Reply-To: <c0c473c1-93af-2a52-bb35-c32f9e96faea@yandex.ru>

On Mon, Dec 7, 2020 at 3:47 AM stsp <stsp2@yandex.ru> wrote:
>
> 07.12.2020 14:29, Paolo Bonzini пишет:
> > On 07/12/20 12:24, stsp wrote:
> >> It tries to enable VME among other things.
> >> qemu appears to disable VME by default,
> >> unless you do "-cpu host". So we have a situation where
> >> the host (which is qemu) doesn't have VME,
> >> and guest (dosemu) is trying to enable it.
> >> Now obviously KVM_SET_CPUID doesn't check anyting
> >> at all and returns success. That later turns
> >> into an invalid guest state.
> >>
> >>
> >> Question: should KVM_SET_CPUID check for
> >> supported bits, end return error if not everything
> >> is supported?
> >
> > No, it is intentional.  Most bits of CPUID are not ever checked by
> > KVM, so userspace is supposed to set values that makes sense
> By "that makes sense" you probably
> meant to say "bits_that_makes_sense masked
> with the ones returned by KVM_GET_SUPPORTED_CPUID"?
>
> So am I right that KVM_SET_CPUID only "lowers"
> the supported bits? In which case I don't need to
> call it at all, but instead just call KVM_GET_SUPPORTED_CPUID
> and see if the needed bits are supported, and
> exit otherwise, right?

"Lowers" is a tricky concept for CPUID information. Some feature bits
report 0 for "present" and 1 for "not-present." Some multi-bit fields
are interpreted as numbers, which may be signed or unsigned. Some
multi-bit fields are strings. Some fields have dependencies on other
fields. Etc.

  parent reply	other threads:[~2020-12-08  0:00 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-07  1:44 [PATCH 0/6] KVM: x86: KVM_SET_SREGS.CR4 bug fixes and cleanup Sean Christopherson
2020-10-07  1:44 ` [PATCH 1/6] KVM: VMX: Drop guest CPUID check for VMXE in vmx_set_cr4() Sean Christopherson
2020-10-07  1:44 ` [PATCH 2/6] KVM: VMX: Drop explicit 'nested' check from vmx_set_cr4() Sean Christopherson
2020-10-07  1:44 ` [PATCH 3/6] KVM: SVM: Drop VMXE check from svm_set_cr4() Sean Christopherson
2020-10-07  1:44 ` [PATCH 4/6] KVM: x86: Move vendor CR4 validity check to dedicated kvm_x86_ops hook Sean Christopherson
2020-10-07  1:44 ` [PATCH 5/6] KVM: x86: Return bool instead of int for CR4 and SREGS validity checks Sean Christopherson
2020-10-07  1:44 ` [PATCH 6/6] KVM: selftests: Verify supported CR4 bits can be set before KVM_SET_CPUID2 Sean Christopherson
2020-10-08 16:00 ` [PATCH 0/6] KVM: x86: KVM_SET_SREGS.CR4 bug fixes and cleanup stsp
2020-10-08 17:59   ` Sean Christopherson
2020-10-08 18:18     ` stsp
2020-10-09  4:04       ` Sean Christopherson
2020-10-09 14:11         ` stsp
2020-10-09 15:30           ` Sean Christopherson
2020-10-09 15:48             ` stsp
2020-10-09 16:11               ` Sean Christopherson
2020-12-07 11:19             ` KVM_SET_CPUID doesn't check supported bits (was Re: [PATCH 0/6] KVM: x86: KVM_SET_SREGS.CR4 bug fixes and cleanup) stsp
2020-12-07 11:24             ` stsp
2020-12-07 11:29               ` Paolo Bonzini
2020-12-07 11:47                 ` stsp
     [not found]                   ` <CABgObfYS57_ez-t=eu9+3S2bhSXC_9DTj=64Sna2jnYEMYo2Ag@mail.gmail.com>
2020-12-07 14:03                     ` stsp
     [not found]                       ` <CABgObfb_4r=k_qakd+48hPar8rzc-P50+dgdoYvQaL2H-po6+g@mail.gmail.com>
2020-12-07 14:29                         ` stsp
     [not found]                           ` <CABgObfYN7Okdt+YfHtsd3M_00iuWf=UyKPmbQhhYBhoiMtdXuw@mail.gmail.com>
2020-12-07 14:41                             ` stsp
2020-12-07 23:59                   ` Jim Mattson [this message]
2020-11-13 11:36 ` [PATCH 0/6] KVM: x86: KVM_SET_SREGS.CR4 bug fixes and cleanup Paolo Bonzini

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CALMp9eSMt1DwXL=wE-xyHcOyCvZzzHdgZ=N9Pqdm1CW6aSzOKw@mail.gmail.com' \
    --to=jmattson@google.com \
    --cc=joro@8bytes.org \
    --cc=kvm@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=pbonzini@redhat.com \
    --cc=sean.j.christopherson@intel.com \
    --cc=stsp2@yandex.ru \
    --cc=vkuznets@redhat.com \
    --cc=wanpengli@tencent.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).