Re: [PATCH] x86/boot: Fix boot failure when SMP MP-table is based at 0

[Tom Lendacky <thomas.lendacky@amd.com>]

On 11/6/2017 2:17 PM, Tom Lendacky wrote:
> When crosvm is used to boot a kernel as a VM, the SMP MP-table is found
> at physical address 0x0. This causes mpf_base to be set to 0 and a
> subsequent "if (!mpf_base)" check in default_get_smp_config() results in
> the MP-table not being parsed.  Further into the boot this results in an
> oops when attempting a read_apic_id().
> 
> Add a boolean variable that is set to true when the MP-table is found.
> Use this variable for testing if the MP-table was found so that even a
> value of 0 for mpf_base will result in continued parsing of the MP-table.
> 
> Reported-by: Tomeu Vizoso <tomeu@tomeuvizoso.net>
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>

I forgot to add a Fixes tag. If the patch is acceptable as is, let me know
if you would prefer another version with the Fixes tag or if you can add
it when merged:

Fixes: 5997efb96756 ("x86/boot: Use memremap() to map the MPF and MPC data")

Thanks,
Tom

> ---
>   arch/x86/kernel/mpparse.c |    6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/mpparse.c b/arch/x86/kernel/mpparse.c
> index 5cbb317..c3d3094 100644
> --- a/arch/x86/kernel/mpparse.c
> +++ b/arch/x86/kernel/mpparse.c
> @@ -430,6 +430,7 @@ static inline void __init construct_default_ISA_mptable(int mpc_default_type)
>   }
>   
>   static unsigned long mpf_base;
> +static bool mpf_found;
>   
>   static unsigned long __init get_mpc_size(unsigned long physptr)
>   {
> @@ -503,7 +504,7 @@ void __init default_get_smp_config(unsigned int early)
>   	if (!smp_found_config)
>   		return;
>   
> -	if (!mpf_base)
> +	if (!mpf_found)
>   		return;
>   
>   	if (acpi_lapic && early)
> @@ -592,6 +593,7 @@ static int __init smp_scan_config(unsigned long base, unsigned long length)
>   			smp_found_config = 1;
>   #endif
>   			mpf_base = base;
> +			mpf_found = true;
>   
>   			pr_info("found SMP MP-table at [mem %#010lx-%#010lx] mapped at [%p]\n",
>   				base, base + sizeof(*mpf) - 1, mpf);
> @@ -857,7 +859,7 @@ static int __init update_mp_table(void)
>   	if (!enable_update_mptable)
>   		return 0;
>   
> -	if (!mpf_base)
> +	if (!mpf_found)
>   		return 0;
>   
>   	mpf = early_memremap(mpf_base, sizeof(*mpf));
>