Re: kvm vmload/vmsave vs tss.ist

[Ingo Molnar]

* Ingo Molnar <mingo@xxxxxxx> wrote:

> i'd suggest to reuse the irq-stacks for this. Right now on 64-bit we've 
> got the following stack layout: 8K process stacks, a 16K IRQ stack on 
> each CPU, shared by all IRQs. Then we have the IST stacks with weird 
> sizes: debug:8K, the others: 4K.

this has to be done carefully though, as there's a subtle detail here: 
right now the pda_irqcount and the pda_irqstackptr logic in entry_64.S is 
not re-entry safe and relies on IRQs being off.

If critical exceptions are moved to the IRQ stack then %rsp switching to 
the IRQ stack has to be done atomically: instead of using the pda_irqcount 
check the %rsp value itself should be checked against pda_irqstackptr - if 
it's within that 16K range then we are already on the IRQ stack and do not 
need to switch to it but can just use the current %rsp.

	Ingo
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