Re: [PATCH v2 15/30] KVM: arm64: Make fault_ipa immutable

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 27/03/26 5:06 PM, Marc Zyngier wrote:
> Updating fault_ipa is conceptually annoying, as it changes something
> that is a property of the fault itself.
> 
> Stop doing so and instead use fault->gfn as the sole piece of state
> that can be used to represent the faulting IPA.
> 
> At the same time, introduce get_canonical_gfn() for the couple of case
> we're we are concerned with the memslot-related IPA and not the faulting
> one.
> 
> Tested-by: Fuad Tabba <tabba@google.com>
> Reviewed-by: Fuad Tabba <tabba@google.com>
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>

>  arch/arm64/kvm/mmu.c | 38 ++++++++++++++++++++++++++------------
>  1 file changed, 26 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 67e5e867e01dc..496bf5903ed3d 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1400,10 +1400,10 @@ static bool fault_supports_stage2_huge_mapping(struct kvm_memory_slot *memslot,
>   */
>  static long
>  transparent_hugepage_adjust(struct kvm *kvm, struct kvm_memory_slot *memslot,
> -			    unsigned long hva, kvm_pfn_t *pfnp,
> -			    phys_addr_t *ipap)
> +			    unsigned long hva, kvm_pfn_t *pfnp, gfn_t *gfnp)
>  {
>  	kvm_pfn_t pfn = *pfnp;
> +	gfn_t gfn = *gfnp;
>  
>  	/*
>  	 * Make sure the adjustment is done only for THP pages. Also make
> @@ -1419,7 +1419,8 @@ transparent_hugepage_adjust(struct kvm *kvm, struct kvm_memory_slot *memslot,
>  		if (sz < PMD_SIZE)
>  			return PAGE_SIZE;
>  
> -		*ipap &= PMD_MASK;
> +		gfn &= ~(PTRS_PER_PMD - 1);
> +		*gfnp = gfn;
>  		pfn &= ~(PTRS_PER_PMD - 1);
>  		*pfnp = pfn;
>  
> @@ -1735,7 +1736,6 @@ static int kvm_s2_fault_get_vma_info(struct kvm_s2_fault *fault)
>  {
>  	struct vm_area_struct *vma;
>  	struct kvm *kvm = fault->vcpu->kvm;
> -	phys_addr_t ipa;
>  
>  	mmap_read_lock(current->mm);
>  	vma = vma_lookup(current->mm, fault->hva);
> @@ -1753,9 +1753,7 @@ static int kvm_s2_fault_get_vma_info(struct kvm_s2_fault *fault)
>  	 * mapping size to ensure we find the right PFN and lay down the
>  	 * mapping in the right place.
>  	 */
> -	fault->fault_ipa = ALIGN_DOWN(fault->fault_ipa, fault->vma_pagesize);
> -	ipa = fault->nested ? kvm_s2_trans_output(fault->nested) : fault->fault_ipa;
> -	fault->gfn = ALIGN_DOWN(ipa, fault->vma_pagesize) >> PAGE_SHIFT;
> +	fault->gfn = ALIGN_DOWN(fault->fault_ipa, fault->vma_pagesize) >> PAGE_SHIFT;
>  
>  	fault->mte_allowed = kvm_vma_mte_allowed(vma);
>  
> @@ -1777,6 +1775,17 @@ static int kvm_s2_fault_get_vma_info(struct kvm_s2_fault *fault)
>  	return 0;
>  }
>  
> +static gfn_t get_canonical_gfn(struct kvm_s2_fault *fault)
> +{
> +	phys_addr_t ipa;
> +
> +	if (!fault->nested)
> +		return fault->gfn;
> +
> +	ipa = kvm_s2_trans_output(fault->nested);
> +	return ALIGN_DOWN(ipa, fault->vma_pagesize) >> PAGE_SHIFT;
> +}
> +
>  static int kvm_s2_fault_pin_pfn(struct kvm_s2_fault *fault)
>  {
>  	int ret;
> @@ -1785,7 +1794,7 @@ static int kvm_s2_fault_pin_pfn(struct kvm_s2_fault *fault)
>  	if (ret)
>  		return ret;
>  
> -	fault->pfn = __kvm_faultin_pfn(fault->memslot, fault->gfn,
> +	fault->pfn = __kvm_faultin_pfn(fault->memslot, get_canonical_gfn(fault),
>  				       fault->write_fault ? FOLL_WRITE : 0,
>  				       &fault->writable, &fault->page);
>  	if (unlikely(is_error_noslot_pfn(fault->pfn))) {
> @@ -1885,6 +1894,11 @@ static int kvm_s2_fault_compute_prot(struct kvm_s2_fault *fault)
>  	return 0;
>  }
>  
> +static phys_addr_t get_ipa(const struct kvm_s2_fault *fault)
> +{
> +	return gfn_to_gpa(fault->gfn);
> +}
> +
>  static int kvm_s2_fault_map(struct kvm_s2_fault *fault, void *memcache)
>  {
>  	struct kvm *kvm = fault->vcpu->kvm;
> @@ -1909,7 +1923,7 @@ static int kvm_s2_fault_map(struct kvm_s2_fault *fault, void *memcache)
>  		} else {
>  			fault->vma_pagesize = transparent_hugepage_adjust(kvm, fault->memslot,
>  									  fault->hva, &fault->pfn,
> -									  &fault->fault_ipa);
> +									  &fault->gfn);
>  
>  			if (fault->vma_pagesize < 0) {
>  				ret = fault->vma_pagesize;
> @@ -1932,10 +1946,10 @@ static int kvm_s2_fault_map(struct kvm_s2_fault *fault, void *memcache)
>  		 * PTE, which will be preserved.
>  		 */
>  		fault->prot &= ~KVM_NV_GUEST_MAP_SZ;
> -		ret = KVM_PGT_FN(kvm_pgtable_stage2_relax_perms)(pgt, fault->fault_ipa,
> +		ret = KVM_PGT_FN(kvm_pgtable_stage2_relax_perms)(pgt, get_ipa(fault),
>  								 fault->prot, flags);
>  	} else {
> -		ret = KVM_PGT_FN(kvm_pgtable_stage2_map)(pgt, fault->fault_ipa, fault->vma_pagesize,
> +		ret = KVM_PGT_FN(kvm_pgtable_stage2_map)(pgt, get_ipa(fault), fault->vma_pagesize,
>  							 __pfn_to_phys(fault->pfn), fault->prot,
>  							 memcache, flags);
>  	}
> @@ -1946,7 +1960,7 @@ static int kvm_s2_fault_map(struct kvm_s2_fault *fault, void *memcache)
>  
>  	/* Mark the page dirty only if the fault is handled successfully */
>  	if (fault->writable && !ret)
> -		mark_page_dirty_in_slot(kvm, fault->memslot, fault->gfn);
> +		mark_page_dirty_in_slot(kvm, fault->memslot, get_canonical_gfn(fault));
>  
>  	if (ret != -EAGAIN)
>  		return ret;