Re: [Xen-devel] [PATCH v3] xen/arm: do not use is_running to decide whether we can write directly to the LR registers

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2013-04-19 at 18:24 +0100, Stefano Stabellini wrote:
> During context switch is_running is set for the next vcpu before the
> gic state is actually saved.
> This leads to possible nasty races when interrupts need to be injected
> after is_running is set to the next vcpu but before the currently
> running gic state has been saved from the previous vcpu.
> 
> Use current instead of is_running to check which one is the currently
> running vcpu: set_current is called right before __context_switch and
> schedule_tail with interrupt disabled.
> 
> Re-enabled interrupts after ctxt_switch_from, so that all the context
> switch saving functions don't have to worry about receiving interrupts
> while saving state.
> 
> Changes in v3:
> - Add a comment in the code to explain why gic_save_state doesn't need a
> spinlock;
> - add an assert in gic_save_state to make sure that interrupts are
> disabled.
> 
> Changes in v2:
> - rework the patch to run ctxt_switch_from with interrupt disabled,
> rather than introducing a gic_running internal variable.
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>

Acked + applied, thanks.



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