netdev - Re: [PATCH 10/13] x86/Swiotlb: Add Swiotlb bounce buffer remap function for HV IVM

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Date:   Fri, 30 Jul 2021 12:10:54 +0800
From:   Tianyu Lan <ltykernel@...il.com>
To:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        wei.liu@...nel.org, decui@...rosoft.com, tglx@...utronix.de,
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Subject: Re: [PATCH 10/13] x86/Swiotlb: Add Swiotlb bounce buffer remap
 function for HV IVM

Hi Konrad:
      Thanks for your review.

On 7/30/2021 12:29 AM, Konrad Rzeszutek Wilk wrote:
>> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
>> index 1fa81c096c1d..6866e5784b53 100644
>> --- a/kernel/dma/swiotlb.c
>> +++ b/kernel/dma/swiotlb.c
>> @@ -194,8 +194,13 @@ static void swiotlb_init_io_tlb_mem(struct io_tlb_mem *mem, phys_addr_t start,
>>   		mem->slots[i].alloc_size = 0;
>>   	}
>>   
>> -	set_memory_decrypted((unsigned long)vaddr, bytes >> PAGE_SHIFT);
>> -	memset(vaddr, 0, bytes);
>> +	mem->vaddr = dma_map_decrypted(vaddr, bytes);
>> +	if (!mem->vaddr) {
>> +		pr_err("Failed to decrypt memory.\n");
> I am wondering if it would be worth returning an error code in this
> function instead of just printing an error?

Yes, this is good idea and will update in the next version.

> 
> For this patch I think it is Ok, but perhaps going forward this would be
> better done as I am thinking - is there some global guest->hyperv
> reporting mechanism so that if this fails - it ends up being bubbled up
> to the HyperV console-ish?

Hyper-V has such panic page report mechanism. Guest can pass one page 
log to host during crash.