linux-kernel - Re: [PATCH v2 16/26] drm/xe/pf: Add helpers for VF GGTT migration data handling

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Message-ID: <8c52f6f4-9356-4511-958a-8c4d6e98f764@intel.com>
Date: Tue, 28 Oct 2025 08:38:20 +0100
From: Michal Wajdeczko <michal.wajdeczko@...el.com>
To: "Tian, Kevin" <kevin.tian@...el.com>, "Winiarski, Michal"
	<michal.winiarski@...el.com>, Alex Williamson <alex.williamson@...hat.com>,
	"De Marchi, Lucas" <lucas.demarchi@...el.com>,
	Thomas Hellström <thomas.hellstrom@...ux.intel.com>, "Vivi,
 Rodrigo" <rodrigo.vivi@...el.com>, Jason Gunthorpe <jgg@...pe.ca>, "Yishai
 Hadas" <yishaih@...dia.com>, "intel-xe@...ts.freedesktop.org"
	<intel-xe@...ts.freedesktop.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"Brost, Matthew" <matthew.brost@...el.com>
CC: "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>, "Jani
 Nikula" <jani.nikula@...ux.intel.com>, Joonas Lahtinen
	<joonas.lahtinen@...ux.intel.com>, Tvrtko Ursulin <tursulin@...ulin.net>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, "Laguna,
 Lukasz" <lukasz.laguna@...el.com>
Subject: Re: [PATCH v2 16/26] drm/xe/pf: Add helpers for VF GGTT migration
 data handling



On 10/28/2025 4:22 AM, Tian, Kevin wrote:
>> From: Winiarski, Michal <michal.winiarski@...el.com>
>> Sent: Wednesday, October 22, 2025 6:41 AM
>>
>> +int xe_ggtt_node_load(struct xe_ggtt_node *node, const void *src, size_t
>> size, u16 vfid)
>> +{
>> +	u64 vfid_pte = xe_encode_vfid_pte(vfid);
>> +	const u64 *buf = src;
>> +	struct xe_ggtt *ggtt;
>> +	u64 start, end;
>> +
>> +	if (!node)
>> +		return -ENOENT;
>> +
>> +	guard(mutex)(&node->ggtt->lock);
>> +
>> +	ggtt = node->ggtt;
>> +	start = node->base.start;
>> +	end = start + size - 1;
>> +
>> +	if (xe_ggtt_pte_size(ggtt, node->base.size) != size)
>> +		return -EINVAL;
>> +
>> +	while (start < end) {
>> +		ggtt->pt_ops->ggtt_set_pte(ggtt, start, (*buf &
>> ~GGTT_PTE_VFID) | vfid_pte);
>> +		start += XE_PAGE_SIZE;
>> +		buf++;
>> +	}
> 
> static u64 xe_encode_vfid_pte(u16 vfid)
> {
>         return FIELD_PREP(GGTT_PTE_VFID, vfid) | XE_PAGE_PRESENT;
> }
> 
> so above loop blindly set every GGTT entry to valid. Isn't the right
> thing to carry the present bit from the src buffer?

VFs can't modify VALID/PRESENT(0) bit so it must be always set by PF

Bspec: 52395