linux-kernel - [PATCH v3 1/2] kvm: arm64: introduce new flag for non-cacheable IO memory

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Date:   Fri, 8 Dec 2023 22:17:08 +0530
From:   <ankita@...dia.com>
To:     <ankita@...dia.com>, <jgg@...dia.com>, <maz@...nel.org>,
        <oliver.upton@...ux.dev>, <suzuki.poulose@....com>,
        <yuzenghui@...wei.com>, <catalin.marinas@....com>,
        <will@...nel.org>, <alex.williamson@...hat.com>,
        <kevin.tian@...el.com>, <yi.l.liu@...el.com>, <ardb@...nel.org>,
        <akpm@...ux-foundation.org>, <gshan@...hat.com>,
        <linux-mm@...ck.org>, <lpieralisi@...nel.org>
CC:     <aniketa@...dia.com>, <cjia@...dia.com>, <kwankhede@...dia.com>,
        <targupta@...dia.com>, <vsethi@...dia.com>, <acurrid@...dia.com>,
        <apopple@...dia.com>, <jhubbard@...dia.com>, <danw@...dia.com>,
        <mochs@...dia.com>, <kvmarm@...ts.linux.dev>,
        <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: [PATCH v3 1/2] kvm: arm64: introduce new flag for non-cacheable IO memory

From: Ankit Agrawal <ankita@...dia.com>

For various reasons described in the cover letter, and primarily to
allow VM get IO memory with NORMALNC properties, it is desired
to relax the KVM stage 2 device memory attributes from DEVICE_nGnRE
to NormalNC. So set S2 PTE for IO memory as NORMAL_NC.

A Normal-NC flag is not present today. So add a new kvm_pgtable_prot
(KVM_PGTABLE_PROT_NORMAL_NC) flag for it, along with its
corresponding PTE value 0x5 (0b101) determined from [1].

Lastly, adapt the stage2 PTE property setter function
(stage2_set_prot_attr) to handle the NormalNC attribute.

[1] section D8.5.5 of DDI0487J_a_a-profile_architecture_reference_manual.pdf

Signed-off-by: Ankit Agrawal <ankita@...dia.com>
Suggested-by: Jason Gunthorpe <jgg@...dia.com>
Acked-by: Catalin Marinas <catalin.marinas@....com>
Tested-by: Ankit Agrawal <ankita@...dia.com>
---
 arch/arm64/include/asm/kvm_pgtable.h |  2 ++
 arch/arm64/include/asm/memory.h      |  2 ++
 arch/arm64/kvm/hyp/pgtable.c         | 11 +++++++++--
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index cfdf40f734b1..19278dfe7978 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -197,6 +197,7 @@ enum kvm_pgtable_stage2_flags {
  * @KVM_PGTABLE_PROT_W:		Write permission.
  * @KVM_PGTABLE_PROT_R:		Read permission.
  * @KVM_PGTABLE_PROT_DEVICE:	Device attributes.
+ * @KVM_PGTABLE_PROT_NORMAL_NC:	Normal noncacheable attributes.
  * @KVM_PGTABLE_PROT_SW0:	Software bit 0.
  * @KVM_PGTABLE_PROT_SW1:	Software bit 1.
  * @KVM_PGTABLE_PROT_SW2:	Software bit 2.
@@ -208,6 +209,7 @@ enum kvm_pgtable_prot {
 	KVM_PGTABLE_PROT_R			= BIT(2),
 
 	KVM_PGTABLE_PROT_DEVICE			= BIT(3),
+	KVM_PGTABLE_PROT_NORMAL_NC		= BIT(4),
 
 	KVM_PGTABLE_PROT_SW0			= BIT(55),
 	KVM_PGTABLE_PROT_SW1			= BIT(56),
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index fde4186cc387..c247e5f29d5a 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -147,6 +147,7 @@
  * Memory types for Stage-2 translation
  */
 #define MT_S2_NORMAL		0xf
+#define MT_S2_NORMAL_NC		0x5
 #define MT_S2_DEVICE_nGnRE	0x1
 
 /*
@@ -154,6 +155,7 @@
  * Stage-2 enforces Normal-WB and Device-nGnRE
  */
 #define MT_S2_FWB_NORMAL	6
+#define MT_S2_FWB_NORMAL_NC	5
 #define MT_S2_FWB_DEVICE_nGnRE	1
 
 #ifdef CONFIG_ARM64_4K_PAGES
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index c651df904fe3..d4835d553c61 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -718,10 +718,17 @@ static int stage2_set_prot_attr(struct kvm_pgtable *pgt, enum kvm_pgtable_prot p
 				kvm_pte_t *ptep)
 {
 	bool device = prot & KVM_PGTABLE_PROT_DEVICE;
-	kvm_pte_t attr = device ? KVM_S2_MEMATTR(pgt, DEVICE_nGnRE) :
-			    KVM_S2_MEMATTR(pgt, NORMAL);
+	bool normal_nc = prot & KVM_PGTABLE_PROT_NORMAL_NC;
+	kvm_pte_t attr;
 	u32 sh = KVM_PTE_LEAF_ATTR_LO_S2_SH_IS;
 
+	if (device)
+		attr = KVM_S2_MEMATTR(pgt, DEVICE_nGnRE);
+	else if (normal_nc)
+		attr = KVM_S2_MEMATTR(pgt, NORMAL_NC);
+	else
+		attr = KVM_S2_MEMATTR(pgt, NORMAL);
+
 	if (!(prot & KVM_PGTABLE_PROT_X))
 		attr |= KVM_PTE_LEAF_ATTR_HI_S2_XN;
 	else if (device)
-- 
2.17.1