Re: [kvm-unit-tests PATCH 08/33] arm: realm: Make uart available before MMU is enabled

Alexandru Elisei
2024-04-22T11:58:53Z

Hi,

On Fri, Apr 12, 2024 at 11:33:43AM +0100, Suzuki K Poulose wrote:
> From: Joey Gouly <joey.gouly@arm.com>
>
> 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@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---
> lib/arm/asm/pgtable.h | 5 +++++
> lib/arm/io.c | 24 +++++++++++++++++++++++-
> lib/arm64/asm/pgtable.h | 5 +++++
> 3 files changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/lib/arm/asm/pgtable.h b/lib/arm/asm/pgtable.h
> index 350039ff..7e85e7c6 100644
> --- a/lib/arm/asm/pgtable.h
> +++ b/lib/arm/asm/pgtable.h
> @@ -112,4 +112,9 @@ static inline pte_t *pte_alloc(pmd_t *pmd, unsigned long addr)
> return pte_offset(pmd, addr);
> }
>
> +static inline unsigned long arm_shared_phys_alias(void *x)
> +{
> + return ((unsigned long)(x) | PTE_NS_SHARED);
> +}

Is it allowed for a realm to run in aarch32 mode?

> +
> #endif /* _ASMARM_PGTABLE_H_ */
> diff --git a/lib/arm/io.c b/lib/arm/io.c
> index 836fa854..127727e4 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"
>
> @@ -30,6 +32,24 @@ static struct spinlock uart_lock;
> static volatile u8 *uart0_base = UART_EARLY_BASE;
> bool is_pl011_uart;
>
> +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_fdt(void)
> {
> /*
> @@ -109,9 +129,11 @@ 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);
> +}

Have you considered specifying the correct UART address at compile time using
./configure --earlycon?

Thanks,
Alex
> +
> /*
> * Highest possible physical address supported.
> */
> --
> 2.34.1
>