Re: [Xen-devel] [PATCH] libxc: remove stale error check for domain size in xc_sr_save_x86_hvm.c

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 26/09/2017 08:33, Juergen Gross wrote:
> Long ago domains to be saved were limited to 1TB size due to the
> migration stream v1 limitations which used a 32 bit value for the
> PFN and the frame type (4 bits) leaving only 28 bits for the PFN.
>
> Migration stream V2 uses a 64 bit value for this purpose, so there
> is no need to refuse saving (or migrating) domains larger than 1 TB.
>
> Remove the related test in xc_sr_save_x86_hvm.c
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>

Sorry, but this still serves a very real purpose.  Without it, you will
crash a 32bit toolstack trying to migrate a large domain, due to virtual
address space exhaustion.

Things are hopefully better now that we don't unconditionally map the
m2p, but iirc, 1.2T domains were the tipping point last time I tried.

I didn't come up with any more clever way of limiting the size, which is
why this check persisted from the legacy code.

~Andrew

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