linux-kernel - Re: alpha: potential race around hae_cache in RESTORE

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Message-ID: <20100927212113.GA20167@jurassic.park.msu.ru>
Date:	Tue, 28 Sep 2010 01:21:13 +0400
From:	Ivan Kokshaysky <ink@...assic.park.msu.ru>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>, rth@...ddle.net,
	linux-kernel@...r.kernel.org, Matt Turner <mattst88@...il.com>
Subject: Re: alpha: potential race around hae_cache in RESTORE_ALL

On Mon, Sep 27, 2010 at 08:01:09PM +0100, Al Viro wrote:
> The only flavours that have HAE at all are APECS, LCA, MCPCIA, JENSEN and
> T2.  APECS, LCA and JENSEN are UP-only, MCPCIA we build with
> MCPCIA_ONE_HAE_WINDOW which blocks HAE switching AFAICS.  So it's really
> about T2 and there we have something interesting:
> 
> #define T2_HAE_1                (IDENT_ADDR + GAMMA_BIAS + 0x38e0000e0UL)
> #define T2_HAE_2                (IDENT_ADDR + GAMMA_BIAS + 0x38e000100UL)
> #define T2_HAE_3                (IDENT_ADDR + GAMMA_BIAS + 0x38e000240UL)
> #define T2_HAE_4                (IDENT_ADDR + GAMMA_BIAS + 0x38e000260UL)
> #define T2_HAE_ADDRESS          T2_HAE_1
> 
> And seeing that it appears to be 4-CPU chipset...

Yeah, looks like per-cpu stuff, but no... From core_t2.c:

	/* Zero HAE.  */                                                        
	*(vulp)T2_HAE_1 = 0; mb(); /* Sparse MEM HAE */                         
	*(vulp)T2_HAE_2 = 0; mb(); /* Sparse I/O HAE */                         
	*(vulp)T2_HAE_3 = 0; mb(); /* Config Space HAE */                       

        /*                                                                      
	* We also now zero out HAE_4, the dense memory HAE, so that            
...

However, a good thing about T2 is that the Sparse HAE window is reasonably
large - 128 Mb, exactly as on MCPCIA. So we can easily do T2_ONE_HAE_WINDOW
and be done with it.

Ivan.
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