linux-kernel - Re: [RFC PATCH 09/28] arm64: RME: RTT handling

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Date: Mon, 18 Mar 2024 11:25:28 +0000
From: Steven Price <steven.price@....com>
To: Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
 kvm@...r.kernel.org, kvmarm@...ts.linux.dev
Cc: Catalin Marinas <catalin.marinas@....com>, Marc Zyngier <maz@...nel.org>,
 Will Deacon <will@...nel.org>, James Morse <james.morse@....com>,
 Oliver Upton <oliver.upton@...ux.dev>,
 Suzuki K Poulose <suzuki.poulose@....com>, Zenghui Yu
 <yuzenghui@...wei.com>, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, Joey Gouly <joey.gouly@....com>,
 Alexandru Elisei <alexandru.elisei@....com>,
 Christoffer Dall <christoffer.dall@....com>, Fuad Tabba <tabba@...gle.com>,
 linux-coco@...ts.linux.dev
Subject: Re: [RFC PATCH 09/28] arm64: RME: RTT handling

On 18/03/2024 11:01, Ganapatrao Kulkarni wrote:
> 
> On 27-01-2023 04:59 pm, Steven Price wrote:
>> The RMM owns the stage 2 page tables for a realm, and KVM must request
>> that the RMM creates/destroys entries as necessary. The physical pages
>> to store the page tables are delegated to the realm as required, and can
>> be undelegated when no longer used.
>>
>> Signed-off-by: Steven Price <steven.price@....com>
>> ---
>>   arch/arm64/include/asm/kvm_rme.h |  19 +++++
>>   arch/arm64/kvm/mmu.c             |   7 +-
>>   arch/arm64/kvm/rme.c             | 139 +++++++++++++++++++++++++++++++
>>   3 files changed, 162 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_rme.h
>> b/arch/arm64/include/asm/kvm_rme.h
>> index a6318af3ed11..eea5118dfa8a 100644
>> --- a/arch/arm64/include/asm/kvm_rme.h
>> +++ b/arch/arm64/include/asm/kvm_rme.h
>> @@ -35,5 +35,24 @@ u32 kvm_realm_ipa_limit(void);
>>   int kvm_realm_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap);
>>   int kvm_init_realm_vm(struct kvm *kvm);
>>   void kvm_destroy_realm(struct kvm *kvm);
>> +void kvm_realm_destroy_rtts(struct realm *realm, u32 ia_bits, u32
>> start_level);
>> +
>> +#define RME_RTT_BLOCK_LEVEL    2
>> +#define RME_RTT_MAX_LEVEL    3
>> +
>> +#define RME_PAGE_SHIFT        12
>> +#define RME_PAGE_SIZE        BIT(RME_PAGE_SHIFT)
> 
> Can we use PAGE_SIZE and PAGE_SHIFT instead of redefining?
> May be we can use them to define RME_PAGE_SIZE and RME_PAGE_SHIFT.

At the moment the code only supports the host page size matching the
RMM's. But I want to leave open the possibility for the host size being
larger than the RMM's. In this case PAGE_SHIFT/PAGE_SIZE will not equal
RME_PAGE_SIZE and RME_PAGE_SHIFT. The host will have to create multiple
RMM RTTs for each host page.

>> +/* See ARM64_HW_PGTABLE_LEVEL_SHIFT() */
>> +#define RME_RTT_LEVEL_SHIFT(l)    \
>> +    ((RME_PAGE_SHIFT - 3) * (4 - (l)) + 3)
> 
> Instead of defining again, can we define to
> ARM64_HW_PGTABLE_LEVEL_SHIFT?

Same as above - ARM64_HW_PGTABLE_LEVEL_SHIFT uses PAGE_SHIFT, but we
want the same calculation using RME_PAGE_SHIFT which might be different.

Thanks,

Steve