linux-kernel - Re: [PATCH 02/17] prmem: write rare for static allocation

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Date:   Fri, 26 Oct 2018 11:41:05 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Igor Stoppa <igor.stoppa@...il.com>
Cc:     Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>,
        Dave Chinner <david@...morbit.com>,
        James Morris <jmorris@...ei.org>,
        Michal Hocko <mhocko@...nel.org>,
        kernel-hardening@...ts.openwall.com,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, igor.stoppa@...wei.com,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Laura Abbott <labbott@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pavel Tatashin <pasha.tatashin@...cle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/17] prmem: write rare for static allocation

On Wed, Oct 24, 2018 at 12:34:49AM +0300, Igor Stoppa wrote:
> +static __always_inline

That's far too large for inline.

> +bool wr_memset(const void *dst, const int c, size_t n_bytes)
> +{
> +	size_t size;
> +	unsigned long flags;
> +	uintptr_t d = (uintptr_t)dst;
> +
> +	if (WARN(!__is_wr_after_init(dst, n_bytes), WR_ERR_RANGE_MSG))
> +		return false;
> +	while (n_bytes) {
> +		struct page *page;
> +		uintptr_t base;
> +		uintptr_t offset;
> +		uintptr_t offset_complement;
> +
> +		local_irq_save(flags);
> +		page = virt_to_page(d);
> +		offset = d & ~PAGE_MASK;
> +		offset_complement = PAGE_SIZE - offset;
> +		size = min(n_bytes, offset_complement);
> +		base = (uintptr_t)vmap(&page, 1, VM_MAP, PAGE_KERNEL);
> +		if (WARN(!base, WR_ERR_PAGE_MSG)) {
> +			local_irq_restore(flags);
> +			return false;
> +		}
> +		memset((void *)(base + offset), c, size);
> +		vunmap((void *)base);

BUG

> +		d += size;
> +		n_bytes -= size;
> +		local_irq_restore(flags);
> +	}
> +	return true;
> +}
> +
> +static __always_inline

Similarly large

> +bool wr_memcpy(const void *dst, const void *src, size_t n_bytes)
> +{
> +	size_t size;
> +	unsigned long flags;
> +	uintptr_t d = (uintptr_t)dst;
> +	uintptr_t s = (uintptr_t)src;
> +
> +	if (WARN(!__is_wr_after_init(dst, n_bytes), WR_ERR_RANGE_MSG))
> +		return false;
> +	while (n_bytes) {
> +		struct page *page;
> +		uintptr_t base;
> +		uintptr_t offset;
> +		uintptr_t offset_complement;
> +
> +		local_irq_save(flags);
> +		page = virt_to_page(d);
> +		offset = d & ~PAGE_MASK;
> +		offset_complement = PAGE_SIZE - offset;
> +		size = (size_t)min(n_bytes, offset_complement);
> +		base = (uintptr_t)vmap(&page, 1, VM_MAP, PAGE_KERNEL);
> +		if (WARN(!base, WR_ERR_PAGE_MSG)) {
> +			local_irq_restore(flags);
> +			return false;
> +		}
> +		__write_once_size((void *)(base + offset), (void *)s, size);
> +		vunmap((void *)base);

Similarly BUG.

> +		d += size;
> +		s += size;
> +		n_bytes -= size;
> +		local_irq_restore(flags);
> +	}
> +	return true;
> +}

> +static __always_inline

Guess what..

> +uintptr_t __wr_rcu_ptr(const void *dst_p_p, const void *src_p)
> +{
> +	unsigned long flags;
> +	struct page *page;
> +	void *base;
> +	uintptr_t offset;
> +	const size_t size = sizeof(void *);
> +
> +	if (WARN(!__is_wr_after_init(dst_p_p, size), WR_ERR_RANGE_MSG))
> +		return (uintptr_t)NULL;
> +	local_irq_save(flags);
> +	page = virt_to_page(dst_p_p);
> +	offset = (uintptr_t)dst_p_p & ~PAGE_MASK;
> +	base = vmap(&page, 1, VM_MAP, PAGE_KERNEL);
> +	if (WARN(!base, WR_ERR_PAGE_MSG)) {
> +		local_irq_restore(flags);
> +		return (uintptr_t)NULL;
> +	}
> +	rcu_assign_pointer((*(void **)(offset + (uintptr_t)base)), src_p);
> +	vunmap(base);

Also still bug.

> +	local_irq_restore(flags);
> +	return (uintptr_t)src_p;
> +}

Also, I see an amount of duplication here that shows you're not nearly
lazy enough.