Re: [Xen-devel] [PATCH v2] viridian: fix assertion failure

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Nov 26, 2018 at 03:38:52PM +0000, Paul Durrant wrote:
> Whilst attempting to crash an apparently wedged Windows domain using
> 'xen-hvmcrash' I managed to trigger the following ASSERT:
> 
> (XEN) Assertion '!vp->ptr' failed at viridian.c:607
> 
> with stack:
> 
> (XEN)    [<ffff82d08032c55d>] viridian_map_guest_page+0x1b4/0x1b6
> (XEN)    [<ffff82d08032b1db>] viridian_synic_load_vcpu_ctxt+0x39/0x3b
> (XEN)    [<ffff82d08032b90d>] viridian.c#viridian_load_vcpu_ctxt+0x93/0xcc
> (XEN)    [<ffff82d0803096d6>] hvm_load+0x10e/0x19e
> (XEN)    [<ffff82d080274c6d>] arch_do_domctl+0xb74/0x25b4
> (XEN)    [<ffff82d0802068ab>] do_domctl+0x16f7/0x19d8
> 
> This happened because viridian_map_guest_page() was not written to cope
> with being called multiple times, but this is unfortunately exactly what
> happens when xen-hvmcrash re-loads the domain context (having clobbered
> the values of RIP).
> 
> This patch simply makes viridian_map_guest_page() return immediately if it
> finds the page already mapped (i.e. vp->ptr != NULL).
> 
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Thanks, Roger.

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