[PATCH] powerpc/svm: Don't issue ultracalls if !mem_encrypt_active()

[Nicholas Piggin]

Excerpts from Will Deacon's message of July 30, 2021 9:42 pm:
> Commit ad6c00283163 ("swiotlb: Free tbl memory in swiotlb_exit()")
> introduced a set_memory_encrypted() call to swiotlb_exit() so that the
> buffer pages are returned to an encrypted state prior to being freed.
> 
> Sachin reports that this leads to the following crash on a Power server:
> 
> [    0.010799] software IO TLB: tearing down default memory pool
> [    0.010805] ------------[ cut here ]------------
> [    0.010808] kernel BUG at arch/powerpc/kernel/interrupt.c:98!
> 
> Nick spotted that this is because set_memory_encrypted() is issuing an
> ultracall which doesn't exist for the processor, and should therefore
> be gated by mem_encrypt_active() to mirror the x86 implementation.
> 
> Cc: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
> Cc: Claire Chang <tientzu at chromium.org>
> Cc: Christoph Hellwig <hch at lst.de>
> Cc: Robin Murphy <robin.murphy at arm.com>
> Fixes: ad6c00283163 ("swiotlb: Free tbl memory in swiotlb_exit()")
> Suggested-by: Nicholas Piggin <npiggin at gmail.com>
> Reported-by: Sachin Sant <sachinp at linux.vnet.ibm.com>
> Tested-by: Sachin Sant <sachinp at linux.vnet.ibm.com>
> Tested-by: Nathan Chancellor <nathan at kernel.org>
> Link: https://lore.kernel.org/r/1905CD70-7656-42AE-99E2-A31FC3812EAC@linux.vnet.ibm.com/
> Signed-off-by: Will Deacon <will at kernel.org>
> ---

Thanks for writing it.

Acked-by: Nicholas Piggin <npiggin at gmail.com>

>  arch/powerpc/platforms/pseries/svm.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/powerpc/platforms/pseries/svm.c b/arch/powerpc/platforms/pseries/svm.c
> index 1d829e257996..87f001b4c4e4 100644
> --- a/arch/powerpc/platforms/pseries/svm.c
> +++ b/arch/powerpc/platforms/pseries/svm.c
> @@ -63,6 +63,9 @@ void __init svm_swiotlb_init(void)
>  
>  int set_memory_encrypted(unsigned long addr, int numpages)
>  {
> +	if (!mem_encrypt_active())
> +		return 0;
> +
>  	if (!PAGE_ALIGNED(addr))
>  		return -EINVAL;
>  
> @@ -73,6 +76,9 @@ int set_memory_encrypted(unsigned long addr, int numpages)
>  
>  int set_memory_decrypted(unsigned long addr, int numpages)
>  {
> +	if (!mem_encrypt_active())
> +		return 0;
> +
>  	if (!PAGE_ALIGNED(addr))
>  		return -EINVAL;
>  
> -- 
> 2.32.0.554.ge1b32706d8-goog
> 
>