Re: [PATCH v4 07/16] x86/cpu: Defer CR pinning setup until after EFI initialization

[Peter Zijlstra]

On Wed, Jul 10, 2024 at 07:06:43PM +0300, Alexander Shishkin wrote:
> In order to map the EFI runtime services, set_virtual_address_map
> needs to be called, which resides in the lower half of the address
> space. This means that LASS needs to be temporarily disabled around
> this call. This can only be done before the CR pinning is set up.
> 
> Move CR pinning setup behind the EFI initialization.
> 
> Signed-off-by: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> Suggested-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>

So the previous patch makes us not boot, and this fixes it up? Perhaps
order things differently?

> ---
>  arch/x86/kernel/cpu/common.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 8aa621dc7d30..c93c59a27dfa 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1948,7 +1948,6 @@ static __init void identify_boot_cpu(void)
>  	enable_sep_cpu();
>  #endif
>  	cpu_detect_tlb(&boot_cpu_data);
> -	setup_cr_pinning();
>  
>  	tsx_init();
>  	tdx_init();
> @@ -2367,10 +2366,16 @@ void __init arch_cpu_finalize_init(void)
>  
>  	/*
>  	 * This needs to follow the FPU initializtion, since EFI depends on it.
> +	 * It also needs to precede the CR pinning setup, because we need to be
> +	 * able to temporarily clear the CR4.LASS bit in order to execute the
> +	 * set_virtual_address_map call, which resides in lower addresses and
> +	 * would trip LASS if enabled.
>  	 */
>  	if (efi_enabled(EFI_RUNTIME_SERVICES))
>  		efi_enter_virtual_mode();
>  
> +	setup_cr_pinning();
> +
>  	/*
>  	 * Ensure that access to the per CPU representation has the initial
>  	 * boot CPU configuration.
> -- 
> 2.43.0
>