linux-kernel - Re: [PATCH v5 02/43] kvm: arm64: pgtable: Track the number of pages in the entry level

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Message-ID: <032d29e7-b6a3-4493-833b-a9b6d9496a75@redhat.com>
Date: Wed, 23 Oct 2024 14:03:03 +1000
From: Gavin Shan <gshan@...hat.com>
To: Steven Price <steven.price@....com>, kvm@...r.kernel.org,
 kvmarm@...ts.linux.dev
Cc: Suzuki K Poulose <suzuki.poulose@....com>,
 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>, 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,
 Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
 Shanker Donthineni <sdonthineni@...dia.com>, Alper Gun
 <alpergun@...gle.com>, "Aneesh Kumar K . V" <aneesh.kumar@...nel.org>
Subject: Re: [PATCH v5 02/43] kvm: arm64: pgtable: Track the number of pages
 in the entry level

On 10/5/24 1:27 AM, Steven Price wrote:
> From: Suzuki K Poulose <suzuki.poulose@....com>
> 
> Keep track of the number of pages allocated for the top level PGD,
> rather than computing it every time (though we need it only twice now).
> This will be used later by Arm CCA KVM changes.
> 
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> Signed-off-by: Steven Price <steven.price@....com>
> ---
>   arch/arm64/include/asm/kvm_pgtable.h | 2 ++
>   arch/arm64/kvm/hyp/pgtable.c         | 5 +++--
>   2 files changed, 5 insertions(+), 2 deletions(-)
> 

If we really want to have the number of pages for the top level PGDs,
the existing helpers kvm_pgtable_stage2_pgd_size() for the same purpose
needs to replaced by (struct kvm_pgtable::pgd_pages << PAGE_SHIFT) and
then removed.

The alternative would be just to use kvm_pgtable_stage2_pgd_size() instead of
introducing struct kvm_pgtable::pgd_pages, which will be used in the slow
paths where realm is created or destroyed.

> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index 03f4c3d7839c..25b512756200 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -404,6 +404,7 @@ static inline bool kvm_pgtable_walk_lock_held(void)
>    * struct kvm_pgtable - KVM page-table.
>    * @ia_bits:		Maximum input address size, in bits.
>    * @start_level:	Level at which the page-table walk starts.
> + * @pgd_pages:		Number of pages in the entry level of the page-table.
>    * @pgd:		Pointer to the first top-level entry of the page-table.
>    * @mm_ops:		Memory management callbacks.
>    * @mmu:		Stage-2 KVM MMU struct. Unused for stage-1 page-tables.
> @@ -414,6 +415,7 @@ static inline bool kvm_pgtable_walk_lock_held(void)
>   struct kvm_pgtable {
>   	u32					ia_bits;
>   	s8					start_level;
> +	u8					pgd_pages;
>   	kvm_pteref_t				pgd;
>   	struct kvm_pgtable_mm_ops		*mm_ops;
>   
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index b11bcebac908..9e1be28c3dc9 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -1534,7 +1534,8 @@ int __kvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm_s2_mmu *mmu,
>   	u32 sl0 = FIELD_GET(VTCR_EL2_SL0_MASK, vtcr);
>   	s8 start_level = VTCR_EL2_TGRAN_SL0_BASE - sl0;
>   
> -	pgd_sz = kvm_pgd_pages(ia_bits, start_level) * PAGE_SIZE;
> +	pgt->pgd_pages = kvm_pgd_pages(ia_bits, start_level);
> +	pgd_sz = pgt->pgd_pages * PAGE_SIZE;
>   	pgt->pgd = (kvm_pteref_t)mm_ops->zalloc_pages_exact(pgd_sz);
>   	if (!pgt->pgd)
>   		return -ENOMEM;
> @@ -1586,7 +1587,7 @@ void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt)
>   	};
>   
>   	WARN_ON(kvm_pgtable_walk(pgt, 0, BIT(pgt->ia_bits), &walker));
> -	pgd_sz = kvm_pgd_pages(pgt->ia_bits, pgt->start_level) * PAGE_SIZE;
> +	pgd_sz = pgt->pgd_pages * PAGE_SIZE;
>   	pgt->mm_ops->free_pages_exact(kvm_dereference_pteref(&walker, pgt->pgd), pgd_sz);
>   	pgt->pgd = NULL;
>   }

Thanks,
Gavin