linux-kernel - Re: [PATCH] crypto: ccp - Clear PSP interrupt status register before calling handler

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Date:   Thu, 6 Apr 2023 16:50:25 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>
Cc:     linux-crypto@...r.kernel.org,
        Tom Lendacky <thomas.lendacky@....com>,
        John Allen <john.allen@....com>,
        Brijesh Singh <brijesh.singh@....com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] crypto: ccp - Clear PSP interrupt status register before
 calling handler

On Tue, Mar 28, 2023 at 03:16:36PM +0000, Jeremi Piotrowski wrote:
> The PSP IRQ is edge-triggered (MSI or MSI-X) in all cases supported by
> the psp module so clear the interrupt status register early in the
> handler to prevent missed interrupts. sev_irq_handler() calls wake_up()
> on a wait queue, which can result in a new command being submitted from
> a different CPU. This then races with the clearing of isr and can result
> in missed interrupts. A missed interrupt results in a command waiting
> until it times out, which results in the psp being declared dead.
> 
> This is unlikely on bare metal, but has been observed when running
> virtualized. In the cases where this is observed, sev->cmdresp_reg has
> PSP_CMDRESP_RESP set which indicates that the command was processed
> correctly but no interrupt was asserted.
> 
> The full sequence of events looks like this:
> 
> CPU 1: submits SEV cmd #1
> CPU 1: calls wait_event_timeout()
> CPU 0: enters psp_irq_handler()
> CPU 0: calls sev_handler()->wake_up()
> CPU 1: wakes up; finishes processing cmd #1
> CPU 1: submits SEV cmd #2
> CPU 1: calls wait_event_timeout()
> PSP:   finishes processing cmd #2; interrupt status is still set; no interrupt
> CPU 0: clears intsts
> CPU 0: exits psp_irq_handler()
> CPU 1: wait_event_timeout() times out; psp_dead=true
> 
> Fixes: 200664d5237f ("crypto: ccp: Add Secure Encrypted Virtualization (SEV) command support")
> Cc: stable@...r.kernel.org
> Signed-off-by: Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>
> ---
>  drivers/crypto/ccp/psp-dev.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)

Patch applied.  Thanks.
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt