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X-MS-Exchange-CrossTenant-Network-Message-Id: 0480a450-b799-424e-4084-08ddda8c4c10 X-MS-Exchange-CrossTenant-AuthSource: PH3PPF9E162731D.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 13 Aug 2025 17:10:26.5804 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: mBDG/LLFZZXS1LShQ3I2P4cKkfqvE4JEdAg7C8OPlBYbo5/JpB5azeUHVQNG2/Od+ORK5h85ufo1O+X2VtPdOg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM3PPF1939049CF X-OriginatorOrg: intel.com X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: BA5E0180002 X-Stat-Signature: pstsbgqm998urynjyhzy5b3ypkwz4kpg X-Rspam-User: X-HE-Tag: 1755105036-886545 X-HE-Meta: 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 mJMK2FHC 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Fuad Tabba wrote: > Hi, > > On Thu, 3 Jul 2025 at 05:12, Michael Roth wrote: > > > > On Wed, Jul 02, 2025 at 05:46:23PM -0700, Vishal Annapurve wrote: > > > On Wed, Jul 2, 2025 at 4:25 PM Michael Roth wrote: > > > > > > > > On Wed, Jun 11, 2025 at 02:51:38PM -0700, Ackerley Tng wrote: > > > > > Michael Roth writes: > > > > > > > > > > > On Wed, May 14, 2025 at 04:41:41PM -0700, Ackerley Tng wrote: [snip] > > > > > > The mtree contents seems to get stored in the same manner in either case so > > > > > > performance-wise only the overhead of a few userspace<->kernel switches > > > > > > would be saved. Are there any other reasons? > > > > > > > > > > > > Otherwise, maybe just settle on SHARED as a documented default (since at > > > > > > least non-CoCo VMs would be able to reliably benefit) and let > > > > > > CoCo/GUEST_MEMFD_FLAG_SUPPORT_SHARED VMs set PRIVATE at whatever > > > > > > granularity makes sense for the architecture/guest configuration. > > > > > > > > > > > > > > > > Because shared pages are split once any memory is allocated, having a > > > > > way to INIT_PRIVATE could avoid the split and then merge on > > > > > conversion. I feel that is enough value to have this config flag, what > > > > > do you think? > > > > > > > > > > I guess we could also have userspace be careful not to do any allocation > > > > > before converting. > > > > (Re-visiting this with the assumption that we *don't* intend to use mmap() to > > populate memory (in which case you can pretty much ignore my previous > > response)) > > > > I'm still not sure where the INIT_PRIVATE flag comes into play. For SNP, > > userspace already defaults to marking everything private pretty close to > > guest_memfd creation time, so the potential for allocations to occur > > in-between seems small, but worth confirming. > > > > But I know in the past there was a desire to ensure TDX/SNP could > > support pre-allocating guest_memfd memory (and even pre-faulting via > > KVM_PRE_FAULT_MEMORY), but I think that could still work right? The > > fallocate() handling could still avoid the split if the whole hugepage > > is private, though there is a bit more potential for that fallocate() > > to happen before userspace does the "manually" shared->private > > conversion. I'll double-check on that aspect, but otherwise, is there > > still any other need for it? > > It's not just about performance. I think that the need is more a > matter of having a consistent API with the hypervisors guest_memfd is > going to support. Memory in guest_memfd is shared by default, but in > pKVM for example, it's private by default. Therefore, it would be good ^^^^^^^^^^^^^^^^ And Coco's as well right? Ira > to have a way to ensure that all guest_memfd allocations can be made > private from the get-go. > > Cheers, > /fuad > [snip]