Re: [PATCH v6 6/8] dma: swiotlb: Centralize memory-encryption pool sizing

[Marek Szyprowski]

On 07.10.2026 12:43, Will Deacon wrote:
> On Wed, Oct 07, 2026 at 11:04:05AM +0100, Catalin Marinas wrote:
>> On Tue, Oct 06, 2026 at 10:49:17PM +0100, Will Deacon wrote:
>>> On Thu, Sep 24, 2026 at 11:37:54AM +0530, Aneesh Kumar K.V (Arm) wrote:
>>>> @@ -496,7 +516,8 @@ swiotlb_select_pool_policy(unsigned int flags)
>>>>  	if (swiotlb_force_disable)
>>>>  		return SWIOTLB_POOL_NONE;
>>>>  
>>>> -	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
>>>> +	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT) &&
>>>> +	    !restricted_dma_pool_present)
>>>>  		return SWIOTLB_POOL_CC_GUEST;
>>> I think this check on the restricted DMA pool is too general -- the pool
>>> could be tied to a specific DMA-capable peripheral and so treating its
>>> presence as a global property isn't right.
>> I agree it's a hack but that was the simplest way to avoid the pVMs
>> getting a bounce buffer after this patch. More than happy to leave it
>> out and reduce the buffer on cmdline or we come up with some better
>> heuristics.
> Hrm, that does mean that reverting just this part will regress pVMs
> because they'll suddenly be allocating a tonne more memory for an
> entirely unused swiotlb buffer. So I think I'd prefer to drop the entire
> series until this has been worked out properly.
I've dropped the entire series from dma-mapping-for-next. Aneesh, please respin
it again and move the pKVM/restricted_dma_pool related code into the separate
patch.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland