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Date: Fri, 12 Sep 2008 17:14:06 -0300
From: Eduardo Habkost <ehabkost@redhat.com>
Message-ID: <20080912201406.GA10147@blackpad>
References: <20080912185856.GM3982@blackpad> <48CAC809.5000901@codemonkey.ws>
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Subject: [Qemu-devel] Re: [PATCH] Make page_find() return 0 for too-large
	addresses
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, gcosta@redhat.com

On Fri, Sep 12, 2008 at 02:50:33PM -0500, Anthony Liguori wrote:
> Eduardo Habkost wrote:
>> On some cases, such as under KVM, tb_invalidate_phys_page_range()
>> may be called for large addresses, when qemu is configured to more than
>> 4GB of RAM.
>>
>> On these cases, qemu was crashing because it was using an index too
>> large for l1_map[], that supports only 32-bit addresses when compiling
>> without CONFIG_USER_ONLY.
>>   
>
> Did you have kqemu enabled in the build?  l1_map should be sufficiently  
> large when you have kqemu disabled.

KVM uses './configure --disable-kqemu', but exec.c has this:

#if defined(CONFIG_USER_ONLY) && defined(TARGET_VIRT_ADDR_SPACE_BITS)
/* XXX: this is a temporary hack for alpha target.
 *      In the future, this is to be replaced by a multi-level table
 *      to actually be able to handle the complete 64 bits address space.
 */
#define L1_BITS (TARGET_VIRT_ADDR_SPACE_BITS - L2_BITS - TARGET_PAGE_BITS)
#else
#define L1_BITS (32 - L2_BITS - TARGET_PAGE_BITS)
#endif


And CONFIG_USER_ONLY is not defined, making l1_map work only for 32-bit
addresses.


BTW, I've just noticed page_find_alloc() has this:

#if TARGET_LONG_BITS > 32
    /* Host memory outside guest VM.  For 32-bit targets we have already
       excluded high addresses.  */
    if (index > ((target_ulong)L2_SIZE * L1_SIZE))
        return NULL;
#endif

So, we can just use a similar check on page_find().


Side note: the check on the kvm git tree looks broken: it is checking
for (L2_SIZE * L1_SIZE * TARGET_PAGE_SIZE) instead.

-- 
Eduardo