Hi Kalesh, On Wed, 02 Mar 2022 17:24:53 +0000, Kalesh Singh <kaleshsingh@xxxxxxxxxx> wrote: > > On Tue, Mar 1, 2022 at 11:46 PM Marc Zyngier <maz@xxxxxxxxxx> wrote: > > > > On Fri, 25 Feb 2022 03:34:47 +0000, > > Kalesh Singh <kaleshsingh@xxxxxxxxxx> wrote: > > > > > > pkvm_hyp_alloc_private_va_range() can be used to reserve private VA ranges > > > in the pKVM nVHE hypervisor (). Also update __pkvm_create_private_mapping() > > > to allow specifying an alignment for the private VA mapping. > > > > > > These will be used to implement stack guard pages for pKVM nVHE hypervisor > > > (in a subsequent patch in the series). > > > > > > Credits to Quentin Perret <qperret@xxxxxxxxxx> for the idea of moving > > > private VA allocation out of __pkvm_create_private_mapping() > > > > > > Signed-off-by: Kalesh Singh <kaleshsingh@xxxxxxxxxx> > > > --- > > > > > > Changes in v4: > > > - Handle null ptr in pkvm_alloc_private_va_range() and replace > > > IS_ERR_OR_NULL checks in callers with IS_ERR checks, per Fuad > > > - Fix kernel-doc comments format, per Fuad > > > - Format __pkvm_create_private_mapping() prototype args (< 80 col), per Fuad > > > > > > Changes in v3: > > > - Handle null ptr in IS_ERR_OR_NULL checks, per Mark > > > > > > Changes in v2: > > > - Allow specifying an alignment for the private VA allocations, per Marc > > > > I probably badly expressed my earlier concern. > > > > Yes, an alignment is necessary. But how often do we want an alignment > > that isn't naturally aligned to the size of the allocation (i.e. the > > power of 2 >= the size of the allocation)? This is what the rest of > > the kernel does (get_order() and co), and I thing we should follow > > this. > > Hi Marc, > > Thanks for clarifying. I think making the alignment implicitly based > on the size here will create unnecessary holes where PAGE_SIZE > alignment would be ok and potentially overflow the private VA space > earlier. Is it not a concern? I don't think we should worry too much about this. Even when building the kernel with a very small VA space (commonly 39 bits), we still have a quarter of that reserved for private EL2 mappings. That's pretty big. We will use a bit more of the memory that is set aside for EL2 page tables, but this shouldn't be a problem either. Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
