From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH v3 15/20] kvm: arm/arm64: Allow tuning the physical address size for VM Date: Wed, 4 Jul 2018 16:51:04 +0100 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-Transfer-Encoding: 8bit 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?= To: Suzuki K Poulose Return-path: Content-Disposition: inline In-Reply-To: <1530270944-11351-16-git-send-email-suzuki.poulose@arm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 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. > > Cc: Marc Zyngier > Cc: Christoffer Dall > Cc: Peter Maydel > Cc: Paolo Bonzini > Cc: Radim Krčmář > 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 > > /* > + * 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 another ioctl, or condense the number of sizes you support instead? Will