From: Paolo Bonzini <pbonzini@redhat.com>
To: Alexander Graf <graf@amazon.de>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
Aaron Lewis <aaronlewis@google.com>, Peter Xu <peterx@redhat.com>,
Sean Christopherson <sean.j.christopherson@intel.com>
Subject: Re: [PATCH] KVM: VMX: Forbid userspace MSR filters for x2APIC
Date: Tue, 20 Oct 2020 13:49:31 +0200 [thread overview]
Message-ID: <ac2be818-04c8-6027-870c-184148e511ef@redhat.com> (raw)
In-Reply-To: <47eb1a4a-d015-b573-d773-e34e578ad753@amazon.de>
On 20/10/20 12:52, Alexander Graf wrote:
>>
>> Yes, but the idea is that x2apic registers are always allowed, even
>> overriding default_allow, and therefore it makes no sense to have them
>> in a range. The patch is only making things fail early for userspace,
>> the policy is defined by Sean's patch.
>
> I don't think we should fail on the following:
>
> {
> default_allow: false,
> ranges: [
> {
> flags: KVM_MSR_FILTER_READ,
> nmsrs: 4096,
> base: 0,
> bitmap: { 1, 1, 1, 1, [...] },
> },
> {
> flags: KVM_MSR_FILTER_READ,
> nmsrs: 4096,
> base: 0xc0000000,
> bitmap: { 1, 1, 1, 1, [...] },
> },
> ],
> }
>
> as a way to say "everything in normal ranges is allowed, the rest please
> deflect". Or even just to set default policies with less ranges.
>
> Or to say it differently: Why can't we just check explicitly after
> setting up all filter lists whether x2apic MSRs are *denied*? If so,
> clear the filter and return -EINVAL.
Hmm, if you start looking at the bitmaps setting up default-deny
policies correctly is almost impossible :/ because you'd have to ensure
that you have at least one range covering the x2apic MSRs. I'll just
document that x2APIC MSRs ignore the filter.
Paolo
next prev parent reply other threads:[~2020-10-20 11:49 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-19 17:05 [PATCH] KVM: VMX: Forbid userspace MSR filters for x2APIC Paolo Bonzini
2020-10-19 17:35 ` Peter Xu
2020-10-19 17:45 ` Graf (AWS), Alexander
2020-10-20 9:27 ` Paolo Bonzini
2020-10-20 9:48 ` Alexander Graf
2020-10-20 10:34 ` Paolo Bonzini
2020-10-20 10:52 ` Alexander Graf
2020-10-20 11:49 ` Paolo Bonzini [this message]
2020-10-21 21:36 Paolo Bonzini
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