From mboxrd@z Thu Jan  1 00:00:00 1970
From: Joerg Roedel <joro@8bytes.org>
Subject: Re: Always false condition in rmap_add
Date: Thu, 11 Nov 2010 22:09:32 +0100
Message-ID: <20101111210931.GF5193@8bytes.org>
References: <AANLkTikhBHe9JEDgY0Jhh86VvoOjV9+KDXB4S6+2_vqV@mail.gmail.com> <AANLkTinK7r=SY8-jcQXTZKbVSLdWEk2K4A8B8yuJ68_o@mail.gmail.com>
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Cc: kvm@vger.kernel.org
To: Prasad Joshi <prasadjoshi124@gmail.com>
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On Thu, Nov 11, 2010 at 06:38:47PM +0000, Prasad Joshi wrote:
> Hello All,
>=20
> I have question on code of rmap_add
>=20
> Here is the code of the function
>=20
> =A0613 static int rmap_add(struct kvm_vcpu *vcpu, u64 *spte, gfn_t gf=
n)
> =A0614 {
>=20
> 624=A0=A0=A0=A0 rmapp =3D gfn_to_rmap(vcpu->kvm, gfn, sp->role.level)=
;
> =A0625=A0=A0=A0=A0 if (!*rmapp) {
> =A0626=A0=A0=A0=A0=A0=A0=A0=A0 rmap_printk("rmap_add: %p %llx 0->1\n"=
, spte, *spte);
> =A0627=A0=A0=A0=A0=A0=A0=A0=A0 *rmapp =3D (unsigned long)spte;
> =A0628=A0=A0=A0=A0 } else if (!(*rmapp & 1)) {
> =A0629=A0=A0=A0=A0=A0=A0=A0=A0 rmap_printk("rmap_add: %p %llx 1->many=
\n", spte, *spte);
> =A0630=A0=A0=A0=A0=A0=A0=A0=A0 desc =3D mmu_alloc_rmap_desc(vcpu);
> =A0631=A0=A0=A0=A0=A0=A0=A0=A0 desc->sptes[0] =3D (u64 *)*rmapp;
> =A0632=A0=A0=A0=A0=A0=A0=A0=A0 desc->sptes[1] =3D spte;
> =A0633=A0=A0=A0=A0=A0=A0=A0=A0 *rmapp =3D (unsigned long)desc | 1;
> =A0634=A0=A0=A0=A0=A0=A0=A0=A0 ++count;
> =A0635=A0=A0=A0=A0 } else {
>=20
> The line 628 checks whether the last bit of the rmapp is 1.
> If it is one then line 633 assigns a new value to rmapp with and sets
> the last bit to 1.

No, line 628 checks if the last bit is not 1, so the check works.

	Joerg