Re: [PATCH v2 1/2] xen: don't allow gnttab_dma_[alloc|free]_pages() in PV guest

["Jürgen Groß" <jgross@suse.com>]

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On 10.11.26 10:59, Andrew Cooper wrote:
> On 10/11/2026 9:56 am, Juergen Gross wrote:
>> Today gnttab_dma_alloc_pages() or gnttab_dma_free_pages are never
>> called when running as a PV guest, but this holds for in-tree callers
>> only.
>>
>> Bail out early when being called in PV mode in order to ensure no out
>> of tree module or future use cases are violating this assumption.
>>
>> This enables to safely remove PV-only code from both functions.
>>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>> ---
>>   drivers/xen/grant-table.c | 11 ++++++-----
>>   1 file changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
>> index 604c4eea5930..56a497987942 100644
>> --- a/drivers/xen/grant-table.c
>> +++ b/drivers/xen/grant-table.c
>> @@ -1063,6 +1063,9 @@ int gnttab_dma_alloc_pages(struct gnttab_dma_alloc_args *args)
>>   	size_t size;
>>   	int i, ret;
>>   
>> +	if (WARN_ON(xen_pv_domain()))
>> +		return -EINVAL;
> 
> This will get very spammy if hit.  WARN_ON_ONCE() ?
I'd rather have it spammy than buried somewhere in the logs.

Additionally I expect any illegal user giving up quite fast if no allocation
at all for DMA is working. :-)


Juergen

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