linux-kernel - [PATCH v2 15/16] arm64: Add a helper to retrieve the PTE of a fixmap

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Date:   Mon,  4 Oct 2021 18:48:48 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     will@...nel.org, qperret@...gle.com, dbrazdil@...gle.com,
        Steven Price <steven.price@....com>,
        Andrew Jones <drjones@...hat.com>,
        Fuad Tabba <tabba@...gle.com>,
        Srivatsa Vaddagiri <vatsa@...eaurora.org>,
        Shanker R Donthineni <sdonthineni@...dia.com>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        kernel-team@...roid.com
Subject: [PATCH v2 15/16] arm64: Add a helper to retrieve the PTE of a fixmap

In order to transfer the early mapping state into KVM's MMIO
guard infrastucture, provide a small helper that will retrieve
the associated PTE.

Signed-off-by: Marc Zyngier <maz@...nel.org>
---
 arch/arm64/include/asm/fixmap.h |  2 ++
 arch/arm64/mm/mmu.c             | 15 +++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/arch/arm64/include/asm/fixmap.h b/arch/arm64/include/asm/fixmap.h
index 4335800201c9..1aae625b944f 100644
--- a/arch/arm64/include/asm/fixmap.h
+++ b/arch/arm64/include/asm/fixmap.h
@@ -105,6 +105,8 @@ void __init early_fixmap_init(void);
 
 extern void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot);
 
+extern pte_t *__get_fixmap_pte(enum fixed_addresses idx);
+
 #include <asm-generic/fixmap.h>
 
 #endif /* !__ASSEMBLY__ */
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index cfd9deb347c3..e7029db5b540 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1286,6 +1286,21 @@ void __set_fixmap(enum fixed_addresses idx,
 	}
 }
 
+pte_t *__get_fixmap_pte(enum fixed_addresses idx)
+{
+	unsigned long addr = __fix_to_virt(idx);
+	pte_t *ptep;
+
+	BUG_ON(idx <= FIX_HOLE || idx >= __end_of_fixed_addresses);
+
+	ptep = fixmap_pte(addr);
+
+	if (!pte_valid(*ptep))
+		return NULL;
+
+	return ptep;
+}
+
 void *__init fixmap_remap_fdt(phys_addr_t dt_phys, int *size, pgprot_t prot)
 {
 	const u64 dt_virt_base = __fix_to_virt(FIX_FDT);
-- 
2.30.2