linux-kernel - Re: [PATCH v3 2/5] KVM: MMU: check guest CR3 reserved bits based on its physical address width.

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Date:   Thu, 24 Aug 2017 23:38:23 +0800
From:   Yu Zhang <yu.c.zhang@...ux.intel.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, rkrcmar@...hat.com,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        xiaoguangrong@...cent.com, joro@...tes.org
Subject: Re: [PATCH v3 2/5] KVM: MMU: check guest CR3 reserved bits based on
 its physical address width.



On 8/24/2017 11:50 PM, Paolo Bonzini wrote:
> On 24/08/2017 17:23, Yu Zhang wrote:
>>>>      static inline u64 rsvd_bits(int s, int e)
>>>>    {
>>>> +    if (e < s)
>>>> +        return 0;
>>>> +
>>>>        return ((1ULL << (e - s + 1)) - 1) << s;
>>>>    }
>>> e = s - 1 is already supported; why do you need e <= s - 2?
>> Sorry? I do not quite understand. When will e = s - 1?
> Is there any case where e < s?  I can see that MAXPHYADDR=63 gives
> rsvd_bits(63, 62), but that works.
>
> In practice, MAXPHYADDR will never be 59 even because the PKRU bits are
> at bits 59..62.

Thanks, Paolo.
I see. I had made an assumption that MAXPHYADDR shall not exceed the 
physical one,
which is 52 I believe. But I'm not sure there's any place to check this.
Maybe we should make sure the vcpu->arch.maxphyaddr will not be greater 
than the
value of the host?

Yu
>
> Paolo
>