linux-kernel - Re: [PATCH RFC 01/10] vmalloc: Add basic perm alloc implementation

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Date:   Fri, 4 Dec 2020 15:24:28 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc:     akpm@...ux-foundation.org, jeyu@...nel.org, bpf@...r.kernel.org,
        ast@...nel.org, daniel@...earbox.net, luto@...nel.org,
        dave.hansen@...ux.intel.com, peterz@...radead.org, x86@...nel.org,
        rppt@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        dan.j.williams@...el.com, elena.reshetova@...el.com,
        ira.weiny@...el.com
Subject: Re: [PATCH RFC 01/10] vmalloc: Add basic perm alloc implementation

On Fri, Nov 20, 2020, Rick Edgecombe wrote:
> +struct perm_allocation {
> +	struct page **pages;
> +	virtual_perm cur_perm;
> +	virtual_perm orig_perm;
> +	struct vm_struct *area;
> +	unsigned long offset;
> +	unsigned long size;
> +	void *writable;
> +};
> +
> +/*
> + * Allocate a special permission kva region. The region may not be mapped
> + * until a call to perm_writable_finish(). A writable region will be mapped
> + * immediately at the address returned by perm_writable_addr(). The allocation
> + * will be made between the start and end virtual addresses.
> + */
> +struct perm_allocation *perm_alloc(unsigned long vstart, unsigned long vend, unsigned long page_cnt,
> +				   virtual_perm perms);

IMO, 'perm' as the root namespace is too generic, and perm_ is already very
prevelant throughout the kernel.  E.g. it's not obvious when looking at the
callers that perm_alloc() is the first step in setting up an alternate kernel
VA->PA mapping.

I don't have a suggestion for a more intuitive name, but in the absence of a
perfect name, I'd vote for an acronym that is easy to grep.  Something like
pvmap?  That isn't currently used in the kernel, though I can't help but read it
as "paravirt map"...