Re: [PATCH v2 1/9] KVM: arm64: Introduce hyp_alloc_private_va_range()

[Mark Rutland <mark.rutland@arm.com>]

On Tue, Feb 22, 2022 at 08:51:02AM -0800, Kalesh Singh wrote:
> hyp_alloc_private_va_range() can be used to reserve private VA ranges
> in the nVHE hypervisor. Also update  __create_hyp_private_mapping()
> to allow specifying an alignment for the private VA mapping.
> 
> These 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>
> ---
>  arch/arm64/include/asm/kvm_mmu.h |  4 +++
>  arch/arm64/kvm/mmu.c             | 61 +++++++++++++++++++++-----------
>  2 files changed, 44 insertions(+), 21 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> index 81839e9a8a24..0b0c71302b92 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -153,6 +153,10 @@ 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);
> +unsigned long hyp_alloc_private_va_range(size_t size, size_t align);
> +int __create_hyp_private_mapping(phys_addr_t phys_addr, size_t size,
> +				size_t align, unsigned long *haddr,
> +				enum kvm_pgtable_prot prot);
>  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 bc2aba953299..e5abcce44ad0 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -457,22 +457,16 @@ 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)
> +
> +/*
> + * Allocates a private VA range below io_map_base.
> + *
> + * @size:	The size of the VA range to reserve.
> + * @align:	The required alignment for the allocation.
> + */
> +unsigned long hyp_alloc_private_va_range(size_t size, size_t align)
>  {
>  	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);

There is a latent bug here; PTR_ERR() is not valid for NULL.

Today on arm64 that will happen to return 0, which may or may not be
what you want, but it's a bad pattern regardless.

That applies to the two copies below that this has been transformed
into.

Thanks,
Mark

> -		*haddr = base;
> -
> -		return 0;
> -	}
>  
>  	mutex_lock(&kvm_hyp_pgd_mutex);
>  
> @@ -484,8 +478,8 @@ 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);
> +	base = ALIGN_DOWN(base, align);
>  
>  	/*
>  	 * Verify that BIT(VA_BITS - 1) hasn't been flipped by
> @@ -493,20 +487,45 @@ static int __create_hyp_private_mapping(phys_addr_t phys_addr, size_t size,
>  	 * overflowed the idmap/IO address range.
>  	 */
>  	if ((base ^ io_map_base) & BIT(VA_BITS - 1))
> -		ret = -ENOMEM;
> +		base = (unsigned long)ERR_PTR(-ENOMEM);
>  	else
>  		io_map_base = base;
>  
>  	mutex_unlock(&kvm_hyp_pgd_mutex);
>  
> +	return base;
> +}
> +
> +int __create_hyp_private_mapping(phys_addr_t phys_addr, size_t size,
> +				size_t align, 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_OR_NULL((void *)addr))
> +			return PTR_ERR((void *)addr);
> +		*haddr = addr;
> +
> +		return 0;
> +	}
> +
> +	size += offset_in_page(phys_addr);
> +	addr = hyp_alloc_private_va_range(size, align);
> +	if (IS_ERR_OR_NULL((void *)addr))
> +		return PTR_ERR((void *)addr);
> +
>  	if (ret)
>  		goto out;
>  
> -	ret = __create_hyp_mappings(base, size, phys_addr, prot);
> +	ret = __create_hyp_mappings(addr, size, phys_addr, prot);
>  	if (ret)
>  		goto out;
>  
> -	*haddr = base + offset_in_page(phys_addr);
> +	*haddr = addr + offset_in_page(phys_addr);
>  out:
>  	return ret;
>  }
> @@ -537,7 +556,7 @@ int create_hyp_io_mappings(phys_addr_t phys_addr, size_t size,
>  		return 0;
>  	}
>  
> -	ret = __create_hyp_private_mapping(phys_addr, size,
> +	ret = __create_hyp_private_mapping(phys_addr, size, PAGE_SIZE,
>  					   &addr, PAGE_HYP_DEVICE);
>  	if (ret) {
>  		iounmap(*kaddr);
> @@ -564,7 +583,7 @@ int create_hyp_exec_mappings(phys_addr_t phys_addr, size_t size,
>  
>  	BUG_ON(is_kernel_in_hyp_mode());
>  
> -	ret = __create_hyp_private_mapping(phys_addr, size,
> +	ret = __create_hyp_private_mapping(phys_addr, size, PAGE_SIZE,
>  					   &addr, PAGE_HYP_EXEC);
>  	if (ret) {
>  		*haddr = NULL;
> -- 
> 2.35.1.473.g83b2b277ed-goog
>