linux-kernel - Re: [PATCH -mm 1/3] i386 boot: replace boot_ioremap with enhanced bt_ioremap

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Message-Id: <1200646105.17230.28.camel@cthulhu.hellion.org.uk>
Date:	Fri, 18 Jan 2008 08:48:25 +0000
From:	Ian Campbell <ijc@...lion.org.uk>
To:	"Huang, Ying" <ying.huang@...el.com>
Cc:	akpm@...ux-foundation.org, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Andi Kleen <ak@...e.de>,
	linux-kernel@...r.kernel.org, Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH -mm 1/3] i386 boot: replace boot_ioremap with enhanced
	bt_ioremap - enhance bt_ioremap


On Tue, 2008-01-15 at 13:45 +0800, Huang, Ying wrote:
> +void __init bt_ioremap_init(void)
> +{
> [...]
> +	*pgd = __pa(bm_pte) | _PAGE_TABLE;
> +}
> [...]
> +static void __init __bt_set_fixmap(enum fixed_addresses idx,
> +				   unsigned long phys, pgprot_t flags)
> +{
> [...]
> +	if (pgprot_val(flags))
> +		*pte = (phys & PAGE_MASK) | pgprot_val(flags);
> +	else
> +		*pte = 0;
[...]

Shouldn't these, and the rest of the file, be using the PTE accessor
macros set_pte,clear_pte etc? The boot_ioremap it replaces seems to have
done. Otherwise these patches don't appear to be paravirt_ops clean. I
haven't had a chance to investigate fully so this might be a Xen bug or
unrelated to this patch but running current x86.git#mm as a Xen guest
ends up with it being shot in the head by the hypervisor with:

        (XEN) Unhandled page fault in domain 16 on VCPU 0 (ec=0000)
        (XEN) Pagetable walk from 00000000f54fe40e:
        (XEN)  L4[0x000] = 000000010c187027 00000000000003b2
        (XEN)  L3[0x003] = 000000010c186027 00000000000003b3
        (XEN)  L2[0x1aa] = 0000000000000000 ffffffffffffffff
        (XEN) domain_crash_sync called from entry.S
        (XEN) Domain 16 (vcpu#0) crashed on cpu#1:
        (XEN) ----[ Xen-3.2.0-rc5  x86_64  debug=y  Not tainted ]----
        (XEN) CPU:    1
        (XEN) RIP:    e019:[<00000000c02601b1>]
        (XEN) RFLAGS: 0000000000000282   CONTEXT: guest
        (XEN) rax: 00000000f54fe40e   rbx: 0000000000005b00   rcx: 0000000000000000
        (XEN) rdx: 0000000000000000   rsi: 0000000000000000   rdi: 00000000c0255b00
        (XEN) rbp: 0000000000000000   rsp: 00000000c0257f68   r8:  0000000000000000
        (XEN) r9:  0000000000000000   r10: 0000000000000000   r11: 0000000000000000
        (XEN) r12: 0000000000000000   r13: 0000000000000000   r14: 0000000000000000
        (XEN) r15: 0000000000000000   cr0: 000000008005003b   cr4: 00000000000006f0
        (XEN) cr3: 000000011b240000   cr2: 00000000f54fe40e
        (XEN) ds: e021   es: e021   fs: e021   gs: e021   ss: e021   cs: e019
        (XEN) Guest stack trace from esp=c0257f68:
        (XEN)   00000000 c02601b1 0001e019 00010082 c0223566 c0257fc8 00000000 c0260675
        (XEN)   c0223566 000002d7 c0257fec c02230fe 00000000 c03af000 c0257fec c02230fe
        (XEN)   00000000 c025ba84 c0203000 c026317f c0257fe4 c0257fe8 c0257fec bfebcbf5
        (XEN)   c02766a0 c03af000 c0257fec c02230fe 00000000 c025f151 9fabc9f5 0000649d
        (XEN)   01020800 00000f44 f5800000 00000000 c03af000 00000000
        
This corresponds to the dereference of *bp in get_bios_ebda():
        static inline unsigned long get_bios_ebda(void)
        {
                unsigned short *bp;
                unsigned long address;
        
                bp = early_ioremap(0x40EUL, 2);
                if (!bp)
                        return 0;
        
                address = *bp;
        

Ian.

-- 
Ian Campbell

Most people can't understand how others can blow their noses differently
than they do.
		-- Turgenev

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