linux-kernel - Re: [PATCH v6 08/17] arm64: hibernate: add trans

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Message-ID: <20191014153419.galjhum7amnyuiml@soleen.tm1wkky2jk1uhgkn0ivaxijq1c.bx.internal.cloudapp.net>
Date:   Mon, 14 Oct 2019 15:34:19 +0000
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     James Morse <james.morse@....com>
Cc:     jmorris@...ei.org, sashal@...nel.org, ebiederm@...ssion.com,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        corbet@....net, catalin.marinas@....com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org, marc.zyngier@....com,
        vladimir.murzin@....com, matthias.bgg@...il.com,
        bhsharma@...hat.com, linux-mm@...ck.org, mark.rutland@....com
Subject: Re: [PATCH v6 08/17] arm64: hibernate: add trans_pgd public functions

> > +
> > +	memcpy(page, src_start, length);
> > +	__flush_icache_range((unsigned long)page, (unsigned long)page + length);
> > +
> > +	trans_pgd = (void *)get_safe_page(GFP_ATOMIC);
> > +	if (!trans_pgd)
> > +		return -ENOMEM;
> > +
> > +	rc = trans_pgd_map_page(trans_pgd, page, dst_addr,
> > +				PAGE_KERNEL_EXEC);
> > +	if (rc)
> > +		return rc;
> > +
> >  	/*
> >  	 * Load our new page tables. A strict BBM approach requires that we
> >  	 * ensure that TLBs are free of any entries that may overlap with the
> 
> (I suspect you are going to to duplicate this in the kexec code. Kexec has the same
> pattern: instructions that have to be copied to do the relocation of the rest of memory)
> 

Yes, the relocation function is also copied, but I do not see an easy
way to unify this particular code with kexec. We can discuss in kexec
part of this series what else can be unified with hibernate's code.

> 
> > @@ -462,6 +476,24 @@ static int copy_page_tables(pgd_t *dst_pgdp, unsigned long start,
> 
> > +int trans_pgd_create_copy(pgd_t **dst_pgdp, unsigned long start,
> > +			  unsigned long end)
> > +{
> > +	int rc;
> > +	pgd_t *trans_pgd = (pgd_t *)get_safe_page(GFP_ATOMIC);
> > +
> > +	if (!trans_pgd) {
> > +		pr_err("Failed to allocate memory for temporary page tables.\n");
> > +		return -ENOMEM;
> > +	}
> > +
> > +	rc = copy_page_tables(trans_pgd, start, end);
> > +	if (!rc)
> > +		*dst_pgdp = trans_pgd;
> 
> *dst_pgdp was already allocated in swsusp_arch_resume().

Good catch, I forgot to remove allocation from swsusp_arch_resume().

 
> > +
> > +	return rc;
> > +}
> > +
> >  /*
> >   * Setup then Resume from the hibernate image using swsusp_arch_suspend_exit().
> >   *
> > @@ -488,7 +520,7 @@ int swsusp_arch_resume(void)
> >  		pr_err("Failed to allocate memory for temporary page tables.\n");
> >  		return -ENOMEM;
> >  	}
> 
> If the allocation moves into 'trans_pgd_create_copy()', please move the code just above
> here (cut off by the diff) that allocates it in swsusp_arch_resume().
> 
> Its actually okay to leak memory like this, hibernate's allocator acts as a memory pool.
> It either gets freed if we fail to resume, or vanishes when the resumed kernel takes over.

I did.

> 
> Reviewed-by: James Morse <james.morse@....com>

Thank you,
Pasha