[RFC PATCH 1/5] KVM: arm64: pgtables: Change write bit from S2AP_W to DBM

[Leonardo Bras <leo.bras@arm.com>]

As a first step of changing the encoding for the Stage2 PTE descriptor,
introduce the DBM bit, and adapt every usage of writable to use the DBM bit
(51) instead of S2AP[1]/Dirty bit (7).

For this step, we convert usages of RW(Dirty) -> WD(DBM|Dirty).

Signed-off-by: Leonardo Bras <leo.bras@arm.com>
---
 arch/arm64/include/asm/kvm_pgtable.h | 3 +++
 arch/arm64/kvm/hyp/pgtable.c         | 8 +++++---
 arch/arm64/kvm/nested.c              | 4 +++-
 arch/arm64/kvm/ptdump.c              | 4 ++--
 4 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 41a8687938eb..37baa86d6fd8 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -86,24 +86,27 @@ typedef u64 kvm_pte_t;
 #define KVM_PTE_LEAF_ATTR_HI		GENMASK(63, 50)
 
 #define KVM_PTE_LEAF_ATTR_HI_SW		GENMASK(58, 55)
 
 #define KVM_PTE_LEAF_ATTR_HI_S1_XN	BIT(54)
 #define KVM_PTE_LEAF_ATTR_HI_S1_UXN	BIT(54)
 #define KVM_PTE_LEAF_ATTR_HI_S1_PXN	BIT(53)
 
 #define KVM_PTE_LEAF_ATTR_HI_S2_XN	GENMASK(54, 53)
 
+#define KVM_PTE_LEAF_ATTR_HI_S2_DBM	BIT(51)
+
 #define KVM_PTE_LEAF_ATTR_HI_S1_GP	BIT(50)
 
 #define KVM_PTE_LEAF_ATTR_S2_PERMS	(KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R | \
 					 KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W | \
+					 KVM_PTE_LEAF_ATTR_HI_S2_DBM | \
 					 KVM_PTE_LEAF_ATTR_HI_S2_XN)
 
 /* pKVM invalid pte encodings */
 #define KVM_INVALID_PTE_TYPE_MASK	GENMASK(63, 60)
 #define KVM_INVALID_PTE_ANNOT_MASK	~(KVM_PTE_VALID | \
 					  KVM_INVALID_PTE_TYPE_MASK)
 
 enum kvm_invalid_pte_type {
 	/*
 	 * Used to indicate a pte for which a 'break-before-make'
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index b74dd5ce1efd..ca49f1bd7c34 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -725,42 +725,43 @@ static int stage2_set_prot_attr(struct kvm_pgtable *pgt, enum kvm_pgtable_prot p
 	}
 
 	r = stage2_set_xn_attr(prot, &attr);
 	if (r)
 		return r;
 
 	if (prot & KVM_PGTABLE_PROT_R)
 		attr |= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R;
 
 	if (prot & KVM_PGTABLE_PROT_W)
-		attr |= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W;
+		attr |= KVM_PTE_LEAF_ATTR_HI_S2_DBM | KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W;
+
 
 	if (!kvm_lpa2_is_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;
 
 	return 0;
 }
 
 enum kvm_pgtable_prot kvm_pgtable_stage2_pte_prot(kvm_pte_t pte)
 {
 	enum kvm_pgtable_prot prot = pte & KVM_PTE_LEAF_ATTR_HI_SW;
 
 	if (!kvm_pte_valid(pte))
 		return prot;
 
 	if (pte & KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R)
 		prot |= KVM_PGTABLE_PROT_R;
-	if (pte & KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W)
+	if (pte & KVM_PTE_LEAF_ATTR_HI_S2_DBM)
 		prot |= KVM_PGTABLE_PROT_W;
 
 	switch (FIELD_GET(KVM_PTE_LEAF_ATTR_HI_S2_XN, pte)) {
 	case 0b00:
 		prot |= KVM_PGTABLE_PROT_PX | KVM_PGTABLE_PROT_UX;
 		break;
 	case 0b01:
 		prot |= KVM_PGTABLE_PROT_UX;
 		break;
 	case 0b11:
@@ -1281,20 +1282,21 @@ static int stage2_update_leaf_attrs(struct kvm_pgtable *pgt, u64 addr,
 		*orig_pte = data.pte;
 
 	if (level)
 		*level = data.level;
 	return 0;
 }
 
 int kvm_pgtable_stage2_wrprotect(struct kvm_pgtable *pgt, u64 addr, u64 size)
 {
 	return stage2_update_leaf_attrs(pgt, addr, size, 0,
+					KVM_PTE_LEAF_ATTR_HI_S2_DBM |
 					KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W,
 					NULL, NULL,
 					KVM_PGTABLE_WALK_IGNORE_EAGAIN);
 }
 
 void kvm_pgtable_stage2_mkyoung(struct kvm_pgtable *pgt, u64 addr,
 				enum kvm_pgtable_walk_flags flags)
 {
 	int ret;
 
@@ -1361,21 +1363,21 @@ int kvm_pgtable_stage2_relax_perms(struct kvm_pgtable *pgt, u64 addr,
 	s8 level;
 	int ret;
 
 	if (prot & KVM_PTE_LEAF_ATTR_HI_SW)
 		return -EINVAL;
 
 	if (prot & KVM_PGTABLE_PROT_R)
 		set |= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R;
 
 	if (prot & KVM_PGTABLE_PROT_W)
-		set |= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W;
+		set |= KVM_PTE_LEAF_ATTR_HI_S2_DBM | KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W;
 
 	if (prot & KVM_PGTABLE_PROT_X) {
 		ret = stage2_set_xn_attr(prot, &xn);
 		if (ret)
 			return ret;
 
 		set |= xn & KVM_PTE_LEAF_ATTR_HI_S2_XN;
 		clr |= ~xn & KVM_PTE_LEAF_ATTR_HI_S2_XN;
 	}
 
diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index 17123f0b6dab..eb8dfffc32c7 100644
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c
@@ -379,21 +379,23 @@ static int walk_nested_s2_pgd(struct kvm_vcpu *vcpu, phys_addr_t ipa,
 	}
 
 	addr_bottom += contiguous_bit_shift(desc, wi, level);
 
 	/* Calculate and return the result */
 	paddr = (desc & GENMASK_ULL(47, addr_bottom)) |
 		(ipa & GENMASK_ULL(addr_bottom - 1, 0));
 	out->output = paddr;
 	out->block_size = 1UL << ((3 - level) * stride + wi->pgshift);
 	out->readable = desc & KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R;
-	out->writable = desc & KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W;
+	/* Takes care of both RO/RW and RO/WC/WD encodings */
+	out->writable = desc & (KVM_PTE_LEAF_ATTR_HI_S2_DBM |
+				KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W);
 	out->level = level;
 	out->desc = desc;
 	return 0;
 }
 
 #define _has_tgran_2(__r, __sz)						\
 	({								\
 		u64 _s1, _s2, _mmfr0 = __r;				\
 									\
 		_s2 = SYS_FIELD_GET(ID_AA64MMFR0_EL1,			\
diff --git a/arch/arm64/kvm/ptdump.c b/arch/arm64/kvm/ptdump.c
index 69899797dbad..b0cb8d84a9e9 100644
--- a/arch/arm64/kvm/ptdump.c
+++ b/arch/arm64/kvm/ptdump.c
@@ -33,22 +33,22 @@ static const struct ptdump_prot_bits stage2_pte_bits[] = {
 		.set	= " ",
 		.clear	= "F",
 	},
 	{
 		.mask	= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R,
 		.val	= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R,
 		.set	= "R",
 		.clear	= " ",
 	},
 	{
-		.mask	= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W,
-		.val	= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W,
+		.mask	= KVM_PTE_LEAF_ATTR_HI_S2_DBM,
+		.val	= KVM_PTE_LEAF_ATTR_HI_S2_DBM,
 		.set	= "W",
 		.clear	= " ",
 	},
 	{
 		.mask	= KVM_PTE_LEAF_ATTR_HI_S2_XN,
 		.val	= 0b00UL << __bf_shf(KVM_PTE_LEAF_ATTR_HI_S2_XN),
 		.set	= "px ux ",
 	},
 	{
 		.mask	= KVM_PTE_LEAF_ATTR_HI_S2_XN,
-- 
2.55.0