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Re: [Xen-devel] [PATCH] x86: store cr4 during suspend/resume

On 10.12.2019 10:59, Andrew Cooper wrote:
> On 09/12/2019 18:06, Roger Pau Monne wrote:
>> Currently cr4 is not cached before suspension, and mmu_cr4_features is
>> used in order to restore the expected cr4 value. This is correct so
>> far because the tasklet that executes the suspend/resume code is
>> running in the idle vCPU context.
>> In order to make the code less fragile, explicitly save the current
>> cr4 value before suspension, so that it can be restored afterwards.
>> This ensures that the cr4 value cached in the cpu_info doesn't get out
>> of sync after resume from suspension.
>> Suggested-by: Jan Beulich <jbeulich@xxxxxxxx>
>> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Why?  There is nothing fragile here.  Suspend/resume is always in idle
> context and loads of other logic already depends on this.
> I've been slowly stripping out redundant saved state like this.

Where it's clearly redundant, this is fine. But I don't think it's
sufficiently clear here, and going back to what was there before
is imo generally less error prone than going to some fixed state.
Furthermore I was hoping we could eventually do away with


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