linux-kernel - Re: [PATCH 1/5] mmu: mark spte present if the x bit is set

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Message-ID: <jpg37nxrqvs.fsf@linux.bootlegged.copy>
Date:	Tue, 28 Jun 2016 16:37:59 -0400
From:	Bandan Das <bsd@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	kvm@...r.kernel.org, guangrong.xiao@...ux.intel.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] mmu: mark spte present if the x bit is set

Paolo Bonzini <pbonzini@...hat.com> writes:

> On 28/06/2016 19:33, Bandan Das wrote:
>>>> >>  static int is_shadow_present_pte(u64 pte)
>>>> >>  {
>>>> >> -	return pte & PT_PRESENT_MASK && !is_mmio_spte(pte);
>>>> >> +	return pte & (PT_PRESENT_MASK | shadow_x_mask) &&
>>>> >> +		!is_mmio_spte(pte);
>>> >
>>> > This should really be pte & 7 when using EPT.  But this is okay as an
>>> > alternative to a new shadow_present_mask.
>> I could revive shadow_xonly_valid probably... Anyway, for now I will
>> add a TODO comment here.
>
> It's okay to it like this, because the only invalid PTEs reaching this
> point are those that is_mmio_spte filters away.  Hence you'll never get
> -W- PTEs here, and pte & 7 is really the same as how you wrote it.  It's
> pretty clever, and doesn't need a TODO at all. :)

Thanks, understood. So, the way it is written now covers all cases for
pte & 7. Let's still add a comment - clever things are usually
confusing to many!

> Paolo