linux-kernel - Re: [PATCH v5 18/18] kvm: arm64: Allow tuning the physical address size for VM

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Date:   Tue, 25 Sep 2018 11:24:13 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Auger Eric <eric.auger@...hat.com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        marc.zyngier@....com, cdall@...nel.org, pbonzini@...hat.com,
        rkrcmar@...hat.com, will.deacon@....com, catalin.marinas@....com,
        james.morse@....com, dave.martin@....com, julien.grall@....com,
        linux-kernel@...r.kernel.org,
        Peter Maydel <peter.maydell@...aro.org>
Subject: Re: [PATCH v5 18/18] kvm: arm64: Allow tuning the physical address
 size for VM

On 09/25/2018 11:00 AM, Auger Eric wrote:
> Hi Suzuki,
> On 9/17/18 12:41 PM, Suzuki K Poulose wrote:
>> Allow specifying the physical address size limit for a new
>> VM via the kvm_type argument for the KVM_CREATE_VM ioctl. This
>> allows us to finalise the stage2 page table as early as possible
>> and hence perform the right checks on the memory slots
>> without complication. The size is ecnoded as Log2(PA_Size) in
> encoded

...

>>
>> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
>> index c664064f76fb..f860251ff27c 100644
>> --- a/Documentation/virtual/kvm/api.txt
>> +++ b/Documentation/virtual/kvm/api.txt
>> @@ -122,6 +122,14 @@ the default trap & emulate implementation (which changes the virtual
>>   memory layout to fit in user mode), check KVM_CAP_MIPS_VZ and use the
>>   flag KVM_VM_MIPS_VZ.
>>   
>> +To configure the physical address space size for a VM (IPA size) on arm64,
>> +check KVM_CAP_ARM_VM_PHYS_SHIFT (which returns the maximum limit for the
>> +IPA shift) and use KVM_VM_TYPE_ARM_PHYS_SHIFT(PHYS_SHIFT). Bits[7-0] of the
>> +machine type has been reserved for specifying the PHYS_SHIFT.
> are reserved to pass the PHYS_SHIFT?
>> +The supported range is [32...IPA_LIMIT], where IPA_LIMIT could be
> s/could be/is



>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>> index 07548de5c988..2a6b29c446db 100644
>> --- a/include/uapi/linux/kvm.h
>> +++ b/include/uapi/linux/kvm.h
>> @@ -750,6 +750,15 @@ struct kvm_ppc_resize_hpt {
>>   
>>   #define KVM_S390_SIE_PAGE_OFFSET 1
>>   
>> +/*
>> + * On arm64, machine type can be used to request the physical
>> + * address size for the VM. Bits[7-0] has been reserved for the PA
> s/has been reserved/are?

Thanks for spotting, fixed all the above.

Suzuki