Re: [Xen-devel] [PATCH] x86/vvmx: Fix deadlock with MSR bitmap merging

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Sent: Thursday, March 12, 2020 2:35 AM
> 
> c/s c47984aabead "nvmx: implement support for MSR bitmaps" introduced a
> use of
> map_domain_page() which may get used in the middle of context switch.
> 
> This is not safe, and causes Xen to deadlock on the mapcache lock:
> 
>   (XEN) Xen call trace:
>   (XEN)    [<ffff82d08022d6ae>] R _spin_lock+0x34/0x5e
>   (XEN)    [<ffff82d0803219d7>] F map_domain_page+0x250/0x527
>   (XEN)    [<ffff82d080356332>] F do_page_fault+0x420/0x780
>   (XEN)    [<ffff82d08038da3d>] F
> x86_64/entry.S#handle_exception_saved+0x68/0x94
>   (XEN)    [<ffff82d08031729f>] F __find_next_zero_bit+0x28/0x69
>   (XEN)    [<ffff82d080321a4d>] F map_domain_page+0x2c6/0x527
>   (XEN)    [<ffff82d08029eeb2>] F nvmx_update_exec_control+0x1d7/0x323
>   (XEN)    [<ffff82d080299f5a>] F vmx_update_cpu_exec_control+0x23/0x40
>   (XEN)    [<ffff82d08029a3f7>] F
> arch/x86/hvm/vmx/vmx.c#vmx_ctxt_switch_from+0xb7/0x121
>   (XEN)    [<ffff82d08031d796>] F
> arch/x86/domain.c#__context_switch+0x124/0x4a9
>   (XEN)    [<ffff82d080320925>] F context_switch+0x154/0x62c
>   (XEN)    [<ffff82d080252f3e>] F
> common/sched/core.c#sched_context_switch+0x16a/0x175
>   (XEN)    [<ffff82d080253877>] F
> common/sched/core.c#schedule+0x2ad/0x2bc
>   (XEN)    [<ffff82d08022cc97>] F common/softirq.c#__do_softirq+0xb7/0xc8
>   (XEN)    [<ffff82d08022cd38>] F do_softirq+0x18/0x1a
>   (XEN)    [<ffff82d0802a2fbb>] F vmx_asm_do_vmentry+0x2b/0x30
> 
> Convert the domheap page into being a xenheap page.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
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