Subject: Re: [PATCH v3 2/5] KVM: MMU: check guest CR3 reserved bits based on
 its physical address width.
To: Paolo Bonzini <pbonzini@redhat.com>, kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, rkrcmar@redhat.com, tglx@linutronix.de,
        mingo@redhat.com, hpa@zytor.com, xiaoguangrong@tencent.com,
        joro@8bytes.org
References: <1503577676-12345-1-git-send-email-yu.c.zhang@linux.intel.com>
 <1503577676-12345-3-git-send-email-yu.c.zhang@linux.intel.com>
 <0bce2df3-79ac-599b-19fa-8ebeaff23623@redhat.com>
 <b4af9303-57bb-76cd-297f-ccb9128daf29@linux.intel.com>
 <35e285e7-168a-25e6-1053-c005da18c103@redhat.com>
From: Yu Zhang <yu.c.zhang@linux.intel.com>
Message-ID: <f772ea78-12cc-7bde-de3c-19aa8aca6251@linux.intel.com>
Date: Thu, 24 Aug 2017 23:38:23 +0800
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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
>