linux-kernel - Re: [PATCH] efi: permit calling efi_mem_reserve

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Date:   Sat, 10 Nov 2018 03:45:14 +0100
From:   "Qian Cai" <cai@....us>
To:     "Ard Biesheuvel" <ard.biesheuvel@...aro.org>
Cc:     linux-mm@...ck.org, linux-efi@...r.kernel.org, will.deacon@....com,
        linux-kernel@...r.kernel.org,
        "Ard Biesheuvel" <ard.biesheuvel@...aro.org>, marc.zyngier@....com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] efi: permit calling efi_mem_reserve_persistent from
 atomic context


On 11/8/18 at 1:05 PM, Ard Biesheuvel wrote:

> Currently, efi_mem_reserve_persistent() may not be called from atomic
> context, since both the kmalloc() call and the memremap() call may
> sleep.
> 
> The kmalloc() call is easy enough to fix, but the memremap() call
> needs to be moved into an init hook since we cannot control the
> memory allocation behavior of memremap() at the call site.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> ---
>  drivers/firmware/efi/efi.c | 31 +++++++++++++++++++------------
>  1 file changed, 19 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index 249eb70691b0..cfc876e0b67b 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -963,36 +963,43 @@ bool efi_is_table_address(unsigned long phys_addr)
>  }
>  
>  static DEFINE_SPINLOCK(efi_mem_reserve_persistent_lock);
> +static struct linux_efi_memreserve *efi_memreserve_root __ro_after_init;
>  
>  int efi_mem_reserve_persistent(phys_addr_t addr, u64 size)
>  {
> -	struct linux_efi_memreserve *rsv, *parent;
> +	struct linux_efi_memreserve *rsv;
>  
> -	if (efi.mem_reserve == EFI_INVALID_TABLE_ADDR)
> +	if (!efi_memreserve_root)
>  		return -ENODEV;
>  
> -	rsv = kmalloc(sizeof(*rsv), GFP_KERNEL);
> +	rsv = kmalloc(sizeof(*rsv), GFP_ATOMIC);
>  	if (!rsv)
>  		return -ENOMEM;
>  
> -	parent = memremap(efi.mem_reserve, sizeof(*rsv), MEMREMAP_WB);
> -	if (!parent) {
> -		kfree(rsv);
> -		return -ENOMEM;
> -	}
> -
>  	rsv->base = addr;
>  	rsv->size = size;
>  
>  	spin_lock(&efi_mem_reserve_persistent_lock);
> -	rsv->next = parent->next;
> -	parent->next = __pa(rsv);
> +	rsv->next = efi_memreserve_root->next;
> +	efi_memreserve_root->next = __pa(rsv);
>  	spin_unlock(&efi_mem_reserve_persistent_lock);
>  
> -	memunmap(parent);
> +	return 0;
> +}
>  
> +static int __init efi_memreserve_root_init(void)
> +{
> +	if (efi.mem_reserve == EFI_INVALID_TABLE_ADDR)
> +		return -ENODEV;
> +
> +	efi_memreserve_root = memremap(efi.mem_reserve,
> +				       sizeof(*efi_memreserve_root),
> +				       MEMREMAP_WB);
> +	if (!efi_memreserve_root)
> +		return -ENOMEM;
>  	return 0;
>  }
> +early_initcall(efi_memreserve_root_init);
>  
>  #ifdef CONFIG_KEXEC
>  static int update_efi_random_seed(struct notifier_block *nb,
> -- 
> 2.19.1
BTW, I won’t be able to apply this patch on top of this series [1]. After applied that series, the original BUG sleep from atomic is gone as well as two other GIC warnings. Do you think a new patch is needed here?

[1] https://www.spinics.net/lists/arm-kernel/msg685751.html