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

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Date:   Mon, 23 Nov 2020 09:00:40 +0000
From:   Christoph Hellwig <hch@...radead.org>
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

First thanks for doing this, having a vmalloc variant that starts out
with proper permissions has been on my todo list for a while.


> +#define PERM_R	1
> +#define PERM_W	2
> +#define PERM_X	4
> +#define PERM_RWX	(PERM_R | PERM_W | PERM_X)
> +#define PERM_RW		(PERM_R | PERM_W)
> +#define PERM_RX		(PERM_R | PERM_X)

Why can't this use the normal pgprot flags?

> +typedef u8 virtual_perm;

This would need __bitwise annotations to allow sparse to typecheck the
flags.

> +/*
> + * 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);

Please avoid totally pointless overly long line (all over the series)

Also I find the unsigned long for kernel virtual address interface
strange, but I'll take a look at the callers later.