linux-kernel - Re: [PATCH v4 09/10] KVM: selftests: Stop memslot creation in KVM internal memslot region

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Date:   Fri, 24 Jan 2020 10:41:55 -0800
From:   Ben Gardon <bgardon@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Cannon Matthews <cannonmatthews@...gle.com>,
        Peter Xu <peterx@...hat.com>,
        Andrew Jones <drjones@...hat.com>,
        Peter Shier <pshier@...gle.com>,
        Oliver Upton <oupton@...gle.com>
Subject: Re: [PATCH v4 09/10] KVM: selftests: Stop memslot creation in KVM
 internal memslot region

On Fri, Jan 24, 2020 at 12:58 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 23/01/20 19:04, Ben Gardon wrote:
> > KVM creates internal memslots covering the region between 3G and 4G in
> > the guest physical address space, when the first vCPU is created.
> > Mapping this region before creation of the first vCPU causes vCPU
> > creation to fail. Prohibit tests from creating such a memslot and fail
> > with a helpful warning when they try to.
> >
> > Signed-off-by: Ben Gardon <bgardon@...gle.com>
> > ---
>
> The internal memslots are much higher than this (0xfffbc000 and
> 0xfee00000).  I'm changing the patch to block 0xfe0000000 and above,
> otherwise it breaks vmx_dirty_log_test.

Perhaps we're working in different units, but I believe paddrs
0xfffbc000 and 0xfee00000 are between 3GiB and 4GiB.
"Proof by Python":
>>> B=1
>>> KB=1024*B
>>> MB=1024*KB
>>> GB=1024*MB
>>> hex(3*GB)
'0xc0000000'
>>> hex(4*GB)
'0x100000000'
>>> 3*GB == 3<<30
True
>>> 0xfffbc000 > 3*GB
True
>>> 0xfffbc000 < 4*GB
True
>>> 0xfee00000 > 3*GB
True
>>> 0xfee00000 < 4*GB
True

Am I missing something?

I don't think blocking 0xfe0000000 and above is useful, as there's
nothing mapped in that region and AFAIK it's perfectly valid to create
memslots there.


>
> Paolo
>