Re: [PATCH v7 1/6] KVM: arm64: Introduce hyp_alloc_private_va_range()

[Marc Zyngier <maz@kernel.org>]

On Fri, 08 Apr 2022 21:03:24 +0100,
Kalesh Singh <kaleshsingh@google.com> wrote:
> 
> hyp_alloc_private_va_range() can be used to reserve private VA ranges
> in the nVHE hypervisor. Allocations are aligned based on the order of
> the requested size.
> 
> This will be used to implement stack guard pages for KVM nVHE hypervisor
> (nVHE Hyp mode / not pKVM), in a subsequent patch in the series.
> 
> Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
> Tested-by: Fuad Tabba <tabba@google.com>
> Reviewed-by: Fuad Tabba <tabba@google.com>
> ---
> 
> Changes in v7:
>   - Add Fuad's Reviewed-by and Tested-by tags.
> 
> Changes in v6:
>   - Update kernel-doc for hyp_alloc_private_va_range()
>     and add return description, per Stephen
>   - Update hyp_alloc_private_va_range() to return an int error code,
>     per Stephen
>   - Replace IS_ERR() checks with IS_ERR_VALUE() check, per Stephen
>   - Clean up goto, per Stephen
> 
> Changes in v5:
>   - Align private allocations based on the order of their size, per Marc
> 
> Changes in v4:
>   - Handle null ptr in hyp_alloc_private_va_range() and replace
>     IS_ERR_OR_NULL checks in callers with IS_ERR checks, per Fuad
>   - Fix kernel-doc comments format, per Fuad
> 
> Changes in v3:
>   - Handle null ptr in IS_ERR_OR_NULL checks, per Mark
> 
> 
>  arch/arm64/include/asm/kvm_mmu.h |  1 +
>  arch/arm64/kvm/mmu.c             | 66 +++++++++++++++++++++-----------
>  2 files changed, 45 insertions(+), 22 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> index 74735a864eee..a50cbb5ba402 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -154,6 +154,7 @@ static __always_inline unsigned long __kern_hyp_va(unsigned long v)
>  int kvm_share_hyp(void *from, void *to);
>  void kvm_unshare_hyp(void *from, void *to);
>  int create_hyp_mappings(void *from, void *to, enum kvm_pgtable_prot prot);
> +int hyp_alloc_private_va_range(size_t size, unsigned long *haddr);
>  int create_hyp_io_mappings(phys_addr_t phys_addr, size_t size,
>  			   void __iomem **kaddr,
>  			   void __iomem **haddr);
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 0d19259454d8..3d3efea4e991 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -457,23 +457,22 @@ int create_hyp_mappings(void *from, void *to, enum kvm_pgtable_prot prot)
>  	return 0;
>  }
>  
> -static int __create_hyp_private_mapping(phys_addr_t phys_addr, size_t size,
> -					unsigned long *haddr,
> -					enum kvm_pgtable_prot prot)
> +
> +/**
> + * hyp_alloc_private_va_range - Allocates a private VA range.
> + * @size:	The size of the VA range to reserve.
> + * @haddr:	The hypervisor virtual start address of the allocation.
> + *
> + * The private virtual address (VA) range is allocated below io_map_base
> + * and aligned based on the order of @size.
> + *
> + * Return: 0 on success or negative error code on failure.
> + */
> +int hyp_alloc_private_va_range(size_t size, unsigned long *haddr)
>  {
>  	unsigned long base;
>  	int ret = 0;
>  
> -	if (!kvm_host_owns_hyp_mappings()) {
> -		base = kvm_call_hyp_nvhe(__pkvm_create_private_mapping,
> -					 phys_addr, size, prot);
> -		if (IS_ERR_OR_NULL((void *)base))
> -			return PTR_ERR((void *)base);
> -		*haddr = base;
> -
> -		return 0;
> -	}
> -
>  	mutex_lock(&kvm_hyp_pgd_mutex);
>  
>  	/*
> @@ -484,30 +483,53 @@ static int __create_hyp_private_mapping(phys_addr_t phys_addr, size_t size,
>  	 *
>  	 * The allocated size is always a multiple of PAGE_SIZE.
>  	 */
> -	size = PAGE_ALIGN(size + offset_in_page(phys_addr));
> -	base = io_map_base - size;
> +	base = io_map_base - PAGE_ALIGN(size);
> +
> +	/* Align the allocation based on the order of its size */
> +	base = ALIGN_DOWN(base, PAGE_SIZE << get_order(size));
>  
>  	/*
>  	 * Verify that BIT(VA_BITS - 1) hasn't been flipped by
>  	 * allocating the new area, as it would indicate we've
>  	 * overflowed the idmap/IO address range.
>  	 */
> -	if ((base ^ io_map_base) & BIT(VA_BITS - 1))
> +	if (!base || (base ^ io_map_base) & BIT(VA_BITS - 1))

I don't get this '!base' check. Why isn't it encompassed by the
'VA_BITS - 1' flip check?

>  		ret = -ENOMEM;
>  	else
> -		io_map_base = base;
> +		*haddr = io_map_base = base;
>  
>  	mutex_unlock(&kvm_hyp_pgd_mutex);
>  
> +	return ret;
> +}
> +
> +static int __create_hyp_private_mapping(phys_addr_t phys_addr, size_t size,
> +					unsigned long *haddr,
> +					enum kvm_pgtable_prot prot)
> +{
> +	unsigned long addr;
> +	int ret = 0;
> +
> +	if (!kvm_host_owns_hyp_mappings()) {
> +		addr = kvm_call_hyp_nvhe(__pkvm_create_private_mapping,
> +					 phys_addr, size, prot);
> +		if (IS_ERR_VALUE(addr))
> +			return addr;
> +		*haddr = addr;
> +
> +		return 0;
> +	}
> +
> +	size += offset_in_page(phys_addr);

This hardly makes any sense on its own. I get it that it is still
doing the right thing as hyp_alloc_private_va_range() will fix it up,
but I'd rather you keep the PAGE_ALIGN() here, even if it ends up
being duplicated.

> +	ret = hyp_alloc_private_va_range(size, &addr);
>  	if (ret)
> -		goto out;
> +		return ret;
>  
> -	ret = __create_hyp_mappings(base, size, phys_addr, prot);
> +	ret = __create_hyp_mappings(addr, size, phys_addr, prot);
>  	if (ret)
> -		goto out;
> +		return ret;
>  
> -	*haddr = base + offset_in_page(phys_addr);
> -out:
> +	*haddr = addr + offset_in_page(phys_addr);
>  	return ret;
>  }
>  

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.