Re: [Xen-devel] [PATCH for-4.12] pvh/dom0: fix deadlock in GSI mapping

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Jan 28, 2019 at 03:22:45PM +0100, Roger Pau Monne wrote:
> The current GSI mapping code can cause the following deadlock:
> 
> (XEN) *** Dumping CPU0 host state: ***
> (XEN) ----[ Xen-4.12.0-rc  x86_64  debug=y   Tainted:  C   ]----
> [...]
> (XEN) Xen call trace:
> (XEN)    [<ffff82d080239852>] vmac.c#_spin_lock_cb+0x32/0x70
> (XEN)    [<ffff82d0802ed40f>] vmac.c#hvm_gsi_assert+0x2f/0x60 <- pick 
> hvm.irq_lock
> (XEN)    [<ffff82d080255cc9>] io.c#hvm_dirq_assist+0xd9/0x130 <- pick 
> event_lock
> (XEN)    [<ffff82d080255b4b>] io.c#dpci_softirq+0xdb/0x120
> (XEN)    [<ffff82d080238ce6>] softirq.c#__do_softirq+0x46/0xa0
> (XEN)    [<ffff82d08026f955>] domain.c#idle_loop+0x35/0x90
> (XEN)
> [...]
> (XEN) *** Dumping CPU3 host state: ***
> (XEN) ----[ Xen-4.12.0-rc  x86_64  debug=y   Tainted:  C   ]----
> [...]
> (XEN) Xen call trace:
> (XEN)    [<ffff82d08023985d>] vmac.c#_spin_lock_cb+0x3d/0x70
> (XEN)    [<ffff82d080281fc8>] vmac.c#allocate_and_map_gsi_pirq+0xc8/0x130 <- 
> pick event_lock
> (XEN)    [<ffff82d0802f44c0>] vioapic.c#vioapic_hwdom_map_gsi+0x80/0x130
> (XEN)    [<ffff82d0802f4399>] vioapic.c#vioapic_write_redirent+0x119/0x1c0 <- 
> pick hvm.irq_lock
> (XEN)    [<ffff82d0802f4075>] vioapic.c#vioapic_write+0x35/0x40
> (XEN)    [<ffff82d0802e96a2>] vmac.c#hvm_process_io_intercept+0xd2/0x230
> (XEN)    [<ffff82d0802e9842>] vmac.c#hvm_io_intercept+0x22/0x50
> (XEN)    [<ffff82d0802dbe9b>] emulate.c#hvmemul_do_io+0x21b/0x3c0
> (XEN)    [<ffff82d0802db302>] emulate.c#hvmemul_do_io_buffer+0x32/0x70
> (XEN)    [<ffff82d0802dcd29>] emulate.c#hvmemul_do_mmio_buffer+0x29/0x30
> (XEN)    [<ffff82d0802dcc19>] emulate.c#hvmemul_phys_mmio_access+0xf9/0x1b0
> (XEN)    [<ffff82d0802dc6d0>] emulate.c#hvmemul_linear_mmio_access+0xf0/0x180
> (XEN)    [<ffff82d0802de971>] emulate.c#hvmemul_linear_mmio_write+0x21/0x30
> (XEN)    [<ffff82d0802de742>] emulate.c#linear_write+0xa2/0x100
> (XEN)    [<ffff82d0802dce15>] emulate.c#hvmemul_write+0xb5/0x120
> (XEN)    [<ffff82d0802babba>] vmac.c#x86_emulate+0x132aa/0x149a0
> (XEN)    [<ffff82d0802c04f9>] vmac.c#x86_emulate_wrapper+0x29/0x70
> (XEN)    [<ffff82d0802db570>] emulate.c#_hvm_emulate_one+0x50/0x140
> (XEN)    [<ffff82d0802e9e31>] vmac.c#hvm_emulate_one_insn+0x41/0x100
> (XEN)    [<ffff82d080345066>] guest_4.o#sh_page_fault__guest_4+0x976/0xd30
> (XEN)    [<ffff82d08030cc69>] vmac.c#vmx_vmexit_handler+0x949/0xea0
> (XEN)    [<ffff82d08031411a>] vmac.c#vmx_asm_vmexit_handler+0xfa/0x270
> 
> In order to solve it move the vioapic_hwdom_map_gsi outside of the
> locked region in vioapic_write_redirent. vioapic_hwdom_map_gsi will
> not access any of the vioapic fields, so there's no need to call the
> function holding the hvm.irq_lock.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Reviewed-by: Wei Liu <wei.liu2@xxxxxxxxxx>

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