Re: [Xen-devel] [PATCH] Misaligned IO reads

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 31 Jul 2006, at 22:29, Ross Maxfield wrote:

> This patch fixes a data corruption bug in hvm_pio_assist() of
> xen/arch/x86/hvm/io.c.  When the OVERLAP flag is set and the guest is
> running in real-mode regs->es is used in the generation of the
> destination address passed to hvm_copy().  regs->es, however, has not
> been initialized and bad happens.  Since __vmread() must be called to
> obtain regs->es to remedy the bug, this patch instead calls __vmread to
> obtain the GUEST_LINEAR_ADDRESS which removes the need to check if the
> guest is in real-mode and hence also the need to adjust addr.  Since
> this block of code is executed so rarely, there is no measurable
> performance impact using this fix for real or protected mode guests.
This is not the right fix -- VMX-specific code in a generic HVM 
function, and it's too localised. I've made an alternative fix in c/s 
10894 which will initialise those extra fields in the regs structure 
for all PIO requests. Please test when it reaches the public tree.
 Thanks,
 Keir


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