linux-kernel - Re: [PATCH v5 2/2] x86/jailhouse: Only enable platform UARTs if available

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Date:   Mon, 7 Oct 2019 18:26:36 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Ralf Ramsauer <ralf.ramsauer@...-regensburg.de>
Cc:     Jan Kiszka <jan.kiszka@...mens.com>, x86@...nel.org,
        jailhouse-dev@...glegroups.com, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v5 2/2] x86/jailhouse: Only enable platform UARTs if
 available

On Mon, Oct 07, 2019 at 02:38:19PM +0200, Ralf Ramsauer wrote:
> ACPI tables aren't available if Linux runs as guest of the hypervisor
> Jailhouse. This makes the 8250 driver probe for all platform UARTs as
> it assumes that all platform are present in case of !ACPI. Jailhouse

I think you mean s/platform/UARTs/ here.

> will stop execution of Linux guest due to port access violation.
> 
> So far, these access violations could be solved by tuning the
> 8250.nr_uarts parameter but it has limitations: We can, e.g., only map

Another "We" you can get rid of.

> consecutive platform UARTs to Linux, and only in the sequence 0x3f8,
> 0x2f8, 0x3e8, 0x2e8.
> 
> Beginning from setup_data version 2, Jailhouse will place information of
> available platform UARTs in setup_data. This allows for selective
> activation of platform UARTs.
> 
> This patch queries the setup_data version and activates only available

s/This patch queries/Query/

> UARTS. It comes with backward compatibility, and will still support
> older setup_data versions. In this case, Linux falls back to the old
> behaviour.
> 
> Signed-off-by: Ralf Ramsauer <ralf.ramsauer@...-regensburg.de>
> ---
>  arch/x86/include/uapi/asm/bootparam.h |  3 +
>  arch/x86/kernel/jailhouse.c           | 83 +++++++++++++++++++++++----
>  2 files changed, 74 insertions(+), 12 deletions(-)

...

> @@ -138,6 +147,53 @@ static int __init jailhouse_pci_arch_init(void)
>  	return 0;
>  }
>  
> +#ifdef CONFIG_SERIAL_8250
> +static bool jailhouse_uart_enabled(unsigned int uart_nr)
> +{
> +	return setup_data.v2.flags & BIT(uart_nr);
> +}
> +
> +static void jailhouse_serial_fixup(int port, struct uart_port *up,
> +				   u32 *capabilities)
> +{
> +	static const u16 pcuart_base[] = {0x3f8, 0x2f8, 0x3e8, 0x2e8};
> +	unsigned int n;
> +
> +	for (n = 0; n < ARRAY_SIZE(pcuart_base); n++) {
> +		if (pcuart_base[n] != up->iobase)
> +			continue;
> +
> +		if (jailhouse_uart_enabled(n)) {
> +			pr_info("Enabling UART%u (port 0x%lx)\n", n,
> +				up->iobase);
> +			jailhouse_setup_irq(up->irq);
> +		} else {
> +			/* Deactivate UART if access isn't allowed */
> +			up->iobase = 0;
> +		}
> +		break;
> +	}
> +}

WARNING: vmlinux.o(.text+0x4fdb0): Section mismatch in reference from the function jailhouse_serial_fixup() to the variable .init.data:can_use_brk_pgt
The function jailhouse_serial_fixup() references
the variable __initdata can_use_brk_pgt.
This is often because jailhouse_serial_fixup lacks a __initdata 
annotation or the annotation of can_use_brk_pgt is wrong.

-- 
Regards/Gruss,
    Boris.

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