Re: [RFC V3 13/13] KVM: arm64: Enable FEAT_LPA2 based 52 bits IPA size on 4K and 16K

[Marc Zyngier]

On Thu, 30 Sep 2021 11:35:16 +0100,
Anshuman Khandual <anshuman.khandual@xxxxxxx> wrote:
> 
> Stage-2 FEAT_LPA2 support is independent and also orthogonal to FEAT_LPA2
> support either in Stage-1 or in the host kernel. Stage-2 IPA range support
> is evaluated from the platform via ID_AA64MMFR0_TGRAN_2_SUPPORTED_LPA2 and
> gets enabled regardless of Stage-1 translation.
> 
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> ---
>  arch/arm64/include/asm/kvm_pgtable.h | 10 +++++++++-
>  arch/arm64/kvm/hyp/pgtable.c         | 25 +++++++++++++++++++++++--
>  arch/arm64/kvm/reset.c               | 14 ++++++++++----
>  3 files changed, 42 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index 0277838..78a9d12 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -29,18 +29,26 @@ typedef u64 kvm_pte_t;
>  
>  #define KVM_PTE_ADDR_MASK		GENMASK(47, PAGE_SHIFT)
>  #define KVM_PTE_ADDR_51_48		GENMASK(15, 12)
> +#define KVM_PTE_ADDR_51_50		GENMASK(9, 8)
>  
>  static inline bool kvm_pte_valid(kvm_pte_t pte)
>  {
>  	return pte & KVM_PTE_VALID;
>  }
>  
> +void set_kvm_lpa2_enabled(void);
> +bool get_kvm_lpa2_enabled(void);
> +
>  static inline u64 kvm_pte_to_phys(kvm_pte_t pte)
>  {
>  	u64 pa = pte & KVM_PTE_ADDR_MASK;
>  
> -	if (PAGE_SHIFT == 16)
> +	if (PAGE_SHIFT == 16) {
>  		pa |= FIELD_GET(KVM_PTE_ADDR_51_48, pte) << 48;
> +	} else {
> +		if (get_kvm_lpa2_enabled())

Having to do a function call just for this test seems bad, specially
for something that is used so often on the fault path.

Why can't this be made a normal capability that indicates LPA support
for the current page size?

> +			pa |= FIELD_GET(KVM_PTE_ADDR_51_50, pte) << 50;

Where are bits 48 and 49?

> +	}
>  
>  	return pa;
>  }
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index f8ceebe..58141bf 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -49,6 +49,18 @@
>  #define KVM_INVALID_PTE_OWNER_MASK	GENMASK(9, 2)
>  #define KVM_MAX_OWNER_ID		1
>  
> +static bool kvm_lpa2_enabled;
> +
> +bool get_kvm_lpa2_enabled(void)
> +{
> +	return kvm_lpa2_enabled;
> +}
> +
> +void set_kvm_lpa2_enabled(void)
> +{
> +	kvm_lpa2_enabled = true;
> +}
> +
>  struct kvm_pgtable_walk_data {
>  	struct kvm_pgtable		*pgt;
>  	struct kvm_pgtable_walker	*walker;
> @@ -126,8 +138,12 @@ static kvm_pte_t kvm_phys_to_pte(u64 pa)
>  {
>  	kvm_pte_t pte = pa & KVM_PTE_ADDR_MASK;
>  
> -	if (PAGE_SHIFT == 16)
> +	if (PAGE_SHIFT == 16) {
>  		pte |= FIELD_PREP(KVM_PTE_ADDR_51_48, pa >> 48);
> +	} else {
> +		if (get_kvm_lpa2_enabled())
> +			pte |= FIELD_PREP(KVM_PTE_ADDR_51_50, pa >> 50);
> +	}
>  
>  	return pte;
>  }
> @@ -540,6 +556,9 @@ u64 kvm_get_vtcr(u64 mmfr0, u64 mmfr1, u32 phys_shift)
>  	 */
>  	vtcr |= VTCR_EL2_HA;
>  
> +	if (get_kvm_lpa2_enabled())
> +		vtcr |= VTCR_EL2_DS;
> +
>  	/* Set the vmid bits */
>  	vtcr |= (get_vmid_bits(mmfr1) == 16) ?
>  		VTCR_EL2_VS_16BIT :
> @@ -577,7 +596,9 @@ static int stage2_set_prot_attr(struct kvm_pgtable *pgt, enum kvm_pgtable_prot p
>  	if (prot & KVM_PGTABLE_PROT_W)
>  		attr |= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W;
>  
> -	attr |= FIELD_PREP(KVM_PTE_LEAF_ATTR_LO_S2_SH, sh);
> +	if (!get_kvm_lpa2_enabled())
> +		attr |= FIELD_PREP(KVM_PTE_LEAF_ATTR_LO_S2_SH, sh);
> +
>  	attr |= KVM_PTE_LEAF_ATTR_LO_S2_AF;
>  	attr |= prot & KVM_PTE_LEAF_ATTR_HI_SW;
>  	*ptep = attr;
> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index 5ce36b0..97ec387 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -315,26 +315,32 @@ u32 get_kvm_ipa_limit(void)
>  
>  int kvm_set_ipa_limit(void)
>  {
> -	unsigned int parange;
> +	unsigned int parange, tgran;
>  	u64 mmfr0;
>  
>  	mmfr0 = read_sanitised_ftr_reg(SYS_ID_AA64MMFR0_EL1);
>  	parange = cpuid_feature_extract_unsigned_field(mmfr0,
>  				ID_AA64MMFR0_PARANGE_SHIFT);
> +	tgran = cpuid_feature_extract_unsigned_field(mmfr0,
> +				ID_AA64MMFR0_TGRAN_2_SHIFT);
>  	/*
>  	 * IPA size beyond 48 bits could not be supported
>  	 * on either 4K or 16K page size. Hence let's cap
>  	 * it to 48 bits, in case it's reported as larger
>  	 * on the system.

Shouldn't you fix this comment?

>  	 */
> -	if (PAGE_SIZE != SZ_64K)
> -		parange = min(parange, (unsigned int)ID_AA64MMFR0_PARANGE_48);
> +	if (PAGE_SIZE != SZ_64K) {
> +		if (tgran == ID_AA64MMFR0_TGRAN_2_SUPPORTED_LPA2)
> +			set_kvm_lpa2_enabled();
> +		else
> +			parange = min(parange, (unsigned int)ID_AA64MMFR0_PARANGE_48);
> +	}
>  
>  	/*
>  	 * Check with ARMv8.5-GTG that our PAGE_SIZE is supported at
>  	 * Stage-2. If not, things will stop very quickly.
>  	 */
> -	switch (cpuid_feature_extract_unsigned_field(mmfr0, ID_AA64MMFR0_TGRAN_2_SHIFT)) {
> +	switch (tgran) {
>  	case ID_AA64MMFR0_TGRAN_2_SUPPORTED_NONE:
>  		kvm_err("PAGE_SIZE not supported at Stage-2, giving up\n");
>  		return -EINVAL;

Another thing I don't see is how you manage TLB invalidation by level
now that we gain a level 0 at 4kB, breaking the current assumptions
encoded in __tlbi_level().

	M.

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