From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60358) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fak34-0007VM-D7 for qemu-devel@nongnu.org; Wed, 04 Jul 2018 11:50:31 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fak31-0000jp-A8 for qemu-devel@nongnu.org; Wed, 04 Jul 2018 11:50:30 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:47116 helo=foss.arm.com) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fak30-0000jL-Sw for qemu-devel@nongnu.org; Wed, 04 Jul 2018 11:50:27 -0400 Date: Wed, 4 Jul 2018 16:51:04 +0100 From: Will Deacon Message-ID: <20180704155104.GN4828@arm.com> References: <1530270944-11351-1-git-send-email-suzuki.poulose@arm.com> <1530270944-11351-16-git-send-email-suzuki.poulose@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1530270944-11351-16-git-send-email-suzuki.poulose@arm.com> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v3 15/20] kvm: arm/arm64: Allow tuning the physical address size for VM List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Suzuki K Poulose Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, james.morse@arm.com, marc.zyngier@arm.com, cdall@kernel.org, eric.auger@redhat.com, julien.grall@arm.com, catalin.marinas@arm.com, punit.agrawal@arm.com, qemu-devel@nongnu.org, Peter Maydel , Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= Hi Suzuki, On Fri, Jun 29, 2018 at 12:15:35PM +0100, Suzuki K Poulose wrote: > Allow specifying the physical address size for a new VM via > the kvm_type argument for KVM_CREATE_VM ioctl. This allows > us to finalise the stage2 page table format as early as possible > and hence perform the right checks on the memory slots without > complication. The size is encoded as Log2(PA_Size) in the bits[7:0] > of the type field and can encode more information in the future if > required. The IPA size is still capped at 40bits. >=20 > Cc: Marc Zyngier > Cc: Christoffer Dall > Cc: Peter Maydel > Cc: Paolo Bonzini > Cc: Radim Kr=C4=8Dm=C3=A1=C5=99 > Signed-off-by: Suzuki K Poulose > --- > arch/arm/include/asm/kvm_mmu.h | 2 ++ > arch/arm64/include/asm/kvm_arm.h | 10 +++------- > arch/arm64/include/asm/kvm_mmu.h | 2 ++ > include/uapi/linux/kvm.h | 10 ++++++++++ > virt/kvm/arm/arm.c | 24 ++++++++++++++++++++++-- > 5 files changed, 39 insertions(+), 9 deletions(-) [...] > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h > index 4df9bb6..fa4cab0 100644 > --- a/include/uapi/linux/kvm.h > +++ b/include/uapi/linux/kvm.h > @@ -751,6 +751,16 @@ struct kvm_ppc_resize_hpt { > #define KVM_S390_SIE_PAGE_OFFSET 1 > =20 > /* > + * On arm/arm64, machine type can be used to request the physical > + * address size for the VM. Bits [7-0] have been reserved for the > + * PA size shift (i.e, log2(PA_Size)). For backward compatibility, > + * value 0 implies the default IPA size, which is 40bits. > + */ > +#define KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK 0xff > +#define KVM_VM_TYPE_ARM_PHYS_SHIFT(x) \ > + ((x) & KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK) This seems like you're allocating quite a lot of bits in a non-extensible interface to a fairly esoteric parameter. Would it be better to add anoth= er ioctl, or condense the number of sizes you support instead? Will