Re: [Xen-devel] xen/arm: Crash when allocating memory for ACPI table (Was Re: Design doc of adding ACPI support for arm64 on Xen - version 2)

[Shannon Zhao <shannon.zhao@xxxxxxxxxx>]

On 2015/8/14 22:41, Julien Grall wrote:
> On 14/08/15 15:35, Shannon Zhao wrote:
> > > > > Do you copy data in the newly allocated memory between 2 xzalloc_bytes?
> > > > No, I just use xzalloc_bytes to allocate some place and copy ACPI to the
> > > > allocated place, modify the content, then call
> > > > raw_copy_to_guest_flush_dcache to copy the modified tables to guest
> > > > memory.
> > > Can you provide the code and show which call is crashing?
> > Oh, sorry. The code is not on hand as it stays at my working computer.
> >  From previous debug, it fails at the xzalloc_bytes. Because I add two
> > printk before and after the xzalloc_bytes, only the before one shows.
> >
> > The code calling route is like below:
> >
> > acpi_create_fadt();
> > acpi_create_gtdt();
> > acpi_create_madt();
> > acpi_create_stao();
> > acpi_create_xsdt();
> > acpi_map_rsdp();
> > acpi_map_rest_table();
> > acpi_create_est();
> > acpi_create_mmap();
> > ...
> >
> > Within everyone of these functions, it will call xzalloc_bytes to
> > allocate memory and call raw_copy_to_guest_flush_dcache to copy the
> > modified tables to guest memory. And this failure happened at
> > acpi_create_xsdt().
> When I asked if you copy data between 2 calls of xzalloc_bytes you said
> no ... But here you say the invert ... So do you copy data between two
> call or not? (FIY, raw_copy_to_guest_flush_dcache is copying data).
Oh, I thought you mean that if I copy data between the two places 
allocated by xzalloc_bytes.
> > If I add xzalloc_bytes(1000) before acpi_create_xsdt() like below:
> >
> > acpi_create_fadt();
> > acpi_create_gtdt();
> > acpi_create_madt();
> > acpi_create_stao();
> >
> > xzalloc_bytes(1000);
> >
> > acpi_create_xsdt();
> > acpi_map_rsdp();
> > acpi_map_rest_table();
> > acpi_create_est();
> > acpi_create_mmap();
> > ...
> >
> > The failure will not happen at acpi_create_xsdt() but at
> > acpi_create_mmap().
> Ok, so it's likely a memory corruption. You need to check the bound you
> ara using when copying the data to the guest or from the ACPI in
> general. Or maybe you just didn't allocate enough space.
But it fails at the xzalloc_bytes itself. not at copy function.

--
Shannon

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