linux-kernel - Re: [PATCH v1 1/4] KVM: MMU: check guest CR3 reserved bits based on its physical address width.

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Date:   Tue, 15 Aug 2017 15:50:36 +0800
From:   Yu Zhang <yu.c.zhang@...ux.intel.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>
Cc:     kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, xiaoguangrong@...cent.com,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH v1 1/4] KVM: MMU: check guest CR3 reserved bits based on
 its physical address width.



On 8/15/2017 12:40 AM, Paolo Bonzini wrote:
> On 14/08/2017 18:13, Jim Mattson wrote:
>>>                  ctxt->ops->get_msr(ctxt, MSR_EFER, &efer);
>>> -               if (efer & EFER_LMA)
>>> -                       rsvd = CR3_L_MODE_RESERVED_BITS & ~CR3_PCID_INVD;
>>> +               if (efer & EFER_LMA) {
>>> +                       u64 maxphyaddr;
>>> +                       u32 eax = 0x80000008;
>>> +
>>> +                       ctxt->ops->get_cpuid(ctxt, &eax, NULL, NULL, NULL);
>>> +                       maxphyaddr = eax * 0xff;
>> What if leaf 0x80000008 is not defined?
> I noticed this too, but I thought it was mitigated by being under
> EFER_LMA.  Unfortunately, kvm_set_efer doesn't check
> guest_cpuid_has_longmode, so I guess you do have to test leaf 0x80000000
> first.  Alternatively:
>
> 1) kvm_cpuid could return false if it's falling back to
> check_cpuid_limit, and emulator_get_cpuid can then be changed to return bool
>
> 2) kvm_cpuid and emulator_get_cpuid could gain a new argument to disable
> the check_cpuid_limit fallback.
>
> Yu, would you like to implement the latter?

Thanks for pointing this out, Jim & Paolo. The latter choice sounds 
better to me. :-)
I'd like to implement this in a separate patch in next version patch set.

Yu
> Paolo
>