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Date: Thu, 25 Dec 2008 19:40:15 +0200 From: Avi Kivity <avi@...hat.com> To: Ingo Molnar <mingo@...e.hu> CC: "H. Peter Anvin" <hpa@...or.com>, Joerg Roedel <joerg.roedel@....com>, Benjamin Serebrin <benjamin.serebrin@....com>, linux-kernel <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org, Alexander Graf <agraf@...e.de>, Arjan van de Ven <arjan@...radead.org>, Alexander van Heukelum <heukelum@...tmail.fm> Subject: Re: kvm vmload/vmsave vs tss.ist Ingo Molnar wrote: > * Ingo Molnar <mingo@...e.hu> 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. > I think it's enough to switch %rsp before incrementing irqcount, no? -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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