Re: [RFC PATCH 02/19] drivers/vhost: Convert to use vm_account

Re: [RFC PATCH 02/19] drivers/vhost: Convert to use vm_account

[Michael S. Tsirkin]

On Tue, Jan 24, 2023 at 04:42:31PM +1100, Alistair Popple wrote:
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index ec32f78..a31dd53 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c

...

> @@ -780,6 +780,10 @@ static int vhost_vdpa_map(struct vhost_vdpa *v, struct vhost_iotlb *iotlb,
>  	u32 asid = iotlb_to_asid(iotlb);
>  	int r = 0;
>  
> +	if (!vdpa->use_va)
> +		if (vm_account_pinned(&dev->vm_account, PFN_DOWN(size)))
> +			return -ENOMEM;
> +
>  	r = vhost_iotlb_add_range_ctx(iotlb, iova, iova + size - 1,
>  				      pa, perm, opaque);
>  	if (r)

I suspect some error handling will have to be reworked then, no?

> -- 
> git-series 0.9.1

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Re: [RFC PATCH 01/19] mm: Introduce vm_account

[Christoph Hellwig]

> +/**
> + * vm_account_init - Initialise a new struct vm_account.
> + * @vm_account: pointer to uninitialised vm_account.
> + * @task: task to charge against.
> + * @user: user to charge against. Must be non-NULL for VM_ACCOUNT_USER.
> + * @flags: flags to use when charging to vm_account.
> + *
> + * Initialise a new uninitialiused struct vm_account. Takes references
> + * on the task/mm/user/cgroup as required although callers must ensure
> + * any references passed in remain valid for the duration of this
> + * call.
> + */
> +void vm_account_init(struct vm_account *vm_account, struct task_struct *task,
> +		struct user_struct *user, enum vm_account_flags flags);


kerneldoc comments are supposed to be next to the implementation, and
not the declaration in the header.

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Re: [RFC PATCH 01/19] mm: Introduce vm_account

[David Hildenbrand]

On 24.01.23 06:42, Alistair Popple wrote:
> Kernel drivers that pin pages should account these pages against
> either user->locked_vm or mm->pinned_vm and fail the pinning if
> RLIMIT_MEMLOCK is exceeded and CAP_IPC_LOCK isn't held.
> 
> Currently drivers open-code this accounting and use various methods to
> update the atomic variables and check against the limits leading to
> various bugs and inconsistencies. To fix this introduce a standard
> interface for charging pinned and locked memory. As this involves
> taking references on kernel objects such as mm_struct or user_struct
> we introduce a new vm_account struct to hold these references. Several
> helper functions are then introduced to grab references and check
> limits.
> 
> As the way these limits are charged and enforced is visible to
> userspace we need to be careful not to break existing applications by
> charging to different counters. As a result the vm_account functions
> support accounting to different counters as required.
> 
> A future change will extend this to also account against a cgroup for
> pinned pages.

The term "vm_account" is misleading, no? VM_ACCOUNT is for accounting 
towards the commit limit ....

-- 
Thanks,

David / dhildenb

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