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Message-ID: <839942af-2b48-a06f-7fc1-6be1ce7cebcd@amd.com>
Date: Wed, 29 Mar 2023 18:19:52 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>,
linux-crypto@...r.kernel.org
Cc: John Allen <john.allen@....com>,
Herbert Xu <herbert@...dor.apana.org.au>,
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 3/28/23 10:16, 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>
Acked-by: Tom Lendacky <thomas.lendacky@....com>
> ---
> drivers/crypto/ccp/psp-dev.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/crypto/ccp/psp-dev.c b/drivers/crypto/ccp/psp-dev.c
> index c9c741ac8442..949a3fa0b94a 100644
> --- a/drivers/crypto/ccp/psp-dev.c
> +++ b/drivers/crypto/ccp/psp-dev.c
> @@ -42,6 +42,9 @@ static irqreturn_t psp_irq_handler(int irq, void *data)
> /* Read the interrupt status: */
> status = ioread32(psp->io_regs + psp->vdata->intsts_reg);
>
> + /* Clear the interrupt status by writing the same value we read. */
> + iowrite32(status, psp->io_regs + psp->vdata->intsts_reg);
> +
> /* invoke subdevice interrupt handlers */
> if (status) {
> if (psp->sev_irq_handler)
> @@ -51,9 +54,6 @@ static irqreturn_t psp_irq_handler(int irq, void *data)
> psp->tee_irq_handler(irq, psp->tee_irq_data, status);
> }
>
> - /* Clear the interrupt status by writing the same value we read. */
> - iowrite32(status, psp->io_regs + psp->vdata->intsts_reg);
> -
> return IRQ_HANDLED;
> }
>
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