linux-kernel - [RFC kvm-unit-tests 07/27] arm: realm: Make uart available before MMU is enabled

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Message-ID: <20230127114108.10025-8-joey.gouly@arm.com>
Date:   Fri, 27 Jan 2023 11:40:48 +0000
From:   Joey Gouly <joey.gouly@....com>
To:     Andrew Jones <andrew.jones@...ux.dev>, <kvmarm@...ts.linux.dev>,
        <kvm@...r.kernel.org>
CC:     <joey.gouly@....com>, Alexandru Elisei <alexandru.elisei@....com>,
        Christoffer Dall <christoffer.dall@....com>,
        Fuad Tabba <tabba@...gle.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Joey Gouly <Joey.Gouly@....com>, Marc Zyngier <maz@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Quentin Perret <qperret@...gle.com>,
        Steven Price <steven.price@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        "Thomas Huth" <thuth@...hat.com>, Will Deacon <will@...nel.org>,
        Zenghui Yu <yuzenghui@...wei.com>,
        <linux-coco@...ts.linux.dev>, <kvmarm@...ts.cs.columbia.edu>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: [RFC kvm-unit-tests 07/27] arm: realm: Make uart available before MMU is enabled

A Realm must access any emulated I/O mappings with the PTE_NS_SHARED bit set.
This is modelled as a PTE attribute, but is actually part of the address.

So, when MMU is disabled, the "physical address" must reflect this bit set. We
access the UART early before the MMU is enabled. So, make sure the UART is
accessed always with the bit set.

Signed-off-by: Joey Gouly <joey.gouly@....com>
---
 lib/arm/io.c            | 24 +++++++++++++++++++++++-
 lib/arm64/asm/pgtable.h |  5 +++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/lib/arm/io.c b/lib/arm/io.c
index 343e1082..f7c6c771 100644
--- a/lib/arm/io.c
+++ b/lib/arm/io.c
@@ -15,6 +15,8 @@
 #include <asm/psci.h>
 #include <asm/spinlock.h>
 #include <asm/io.h>
+#include <asm/mmu-api.h>
+#include <asm/pgtable.h>
 
 #include "io.h"
 
@@ -29,6 +31,24 @@ static struct spinlock uart_lock;
 #define UART_EARLY_BASE (u8 *)(unsigned long)CONFIG_UART_EARLY_BASE
 static volatile u8 *uart0_base = UART_EARLY_BASE;
 
+static inline volatile u8 *get_uart_base(void)
+{
+	/*
+	 * The address of the UART base may be different
+	 * based on whether we are running with/without
+	 * MMU enabled.
+	 *
+	 * For realms, we must force to use the shared physical
+	 * alias with MMU disabled, to make sure the I/O can
+	 * be emulated.
+	 * When the MMU is turned ON, the mappings are created
+	 * appropriately.
+	 */
+	if (mmu_enabled())
+		return uart0_base;
+	return (u8 *)arm_shared_phys_alias((void *)uart0_base);
+}
+
 static void uart0_init(void)
 {
 	/*
@@ -81,9 +101,11 @@ void io_init(void)
 
 void puts(const char *s)
 {
+	volatile u8 *uart_base = get_uart_base();
+
 	spin_lock(&uart_lock);
 	while (*s)
-		writeb(*s++, uart0_base);
+		writeb(*s++, uart_base);
 	spin_unlock(&uart_lock);
 }
 
diff --git a/lib/arm64/asm/pgtable.h b/lib/arm64/asm/pgtable.h
index 5b9f40b0..871c03e9 100644
--- a/lib/arm64/asm/pgtable.h
+++ b/lib/arm64/asm/pgtable.h
@@ -28,6 +28,11 @@ extern unsigned long prot_ns_shared;
 */
 #define PTE_NS_SHARED		(prot_ns_shared)
 
+static inline unsigned long arm_shared_phys_alias(void *addr)
+{
+	return ((unsigned long)addr | PTE_NS_SHARED);
+}
+
 /*
  * Highest possible physical address supported.
  */
-- 
2.17.1