Re: [Xen-devel] [PATCH v5 05/12] x86: provide executable fixmap facility

From: Wei Liu <wl@xen.org>
To: Xen Development List <xen-devel@lists.xenproject.org>
Cc: "Wei Liu" <liuwe@microsoft.com>, "Wei Liu" <wl@xen.org>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Paul Durrant" <pdurrant@amazon.com>,
	"Michael Kelley" <mikelley@microsoft.com>,
	"Ross Lagerwall" <ross.lagerwall@citrix.com>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH v5 05/12] x86: provide executable fixmap facility
Date: Fri, 31 Jan 2020 13:12:15 +0000	[thread overview]
Message-ID: <20200131131215.bc7daxfbasudiwbi@debian> (raw)
In-Reply-To: <20200130003047.pg3dxgy4vtqjhayo@debian>

On Thu, Jan 30, 2020 at 12:30:47AM +0000, Wei Liu wrote:
> On Wed, Jan 29, 2020 at 08:20:27PM +0000, Wei Liu wrote:
> >  
> > +void __set_fixmap_x(
> > +    enum fixed_addresses_x idx, unsigned long mfn, unsigned long flags)
> > +{
> > +    BUG_ON(idx >= __end_of_fixed_addresses_x || idx <= FIX_X_RESERVED);
> > +    map_pages_to_xen(__fix_x_to_virt(idx), _mfn(mfn), 1, flags);
> > +
> > +    /* Generate a symbol to be used in linker script */
> > +    asm ( ".equ FIXADDR_X_SIZE, %c0; .global FIXADDR_X_SIZE"
> > +          :: "i" (__end_of_fixed_addresses_x << PAGE_SHIFT) );
> 
> The (__end << SHIFT) part can be replaced with FIXADDR_X_SIZE (the macro
> defined in fixmap.h) directly.

I also discover that this snippet to generate symbol should be moved
else where because if Hyper-V support is compiled out, this function has
no user. That causes it to be DCE'd. FIXADDR_X_SIZE would be gone and
linking would fail.

I have moved this to arch_init_memory. Its storage will be reclaimed
during runtime, but this symbol is not used anywhere else in code, so we
should be fine.

Wei.

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