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Date:   Tue, 18 Jan 2022 13:08:31 +0100
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Subject: Re: [PATCH 0/5] kvm: fix latent guest entry/exit bugs
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To:     Mark Rutland <mark.rutland@arm.com>,
        Paolo Bonzini <pbonzini@redhat.com>
Cc:     linux-kernel@vger.kernel.org, aleksandar.qemu.devel@gmail.com,
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From:   Christian Borntraeger <borntraeger@linux.ibm.com>
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Am 18.01.22 um 13:02 schrieb Mark Rutland:
> On Mon, Jan 17, 2022 at 06:45:36PM +0100, Paolo Bonzini wrote:
>> On 1/14/22 16:19, Mark Rutland wrote:
>>> I also think there is another issue here. When an IRQ is taken from SIE, will
>>> user_mode(regs) always be false, or could it be true if the guest userspace is
>>> running? If it can be true I think tha context tracking checks can complain,
>>> and it*might*  be possible to trigger a panic().
>>
>> I think that it would be false, because the guest PSW is in the SIE block
>> and switched on SIE entry and exit, but I might be incorrect.
> 
> Ah; that's the crux of my confusion: I had thought the guest PSW would
> be placed in the regular lowcore *_old_psw slots. From looking at the
> entry asm it looks like the host PSW (around the invocation of SIE) is
> stored there, since that's what the OUTSIDE + SIEEXIT handling is
> checking for.

Yes, Paolos observation is correct.
> 
> Assuming that's correct, I agree this problem doesn't exist, and there's
> only the common RCU/tracing/lockdep management to fix.
> 
> Sorry for the noise, and thanks for the pointer!
> 
> Thanks,
> Mark.