crypto: ccp - Fix command completion detection race

The wait_event() function is used to detect command completion.  The
interrupt handler will set the wait condition variable when the interrupt
is triggered.  However, the variable used for wait_event() is initialized
after the command has been submitted, which can create a race condition
with the interrupt handler and result in the wait_event() never returning.
Move the initialization of the wait condition variable to just before
command submission.

Fixes: 200664d5 ("crypto: ccp: Add Secure Encrypted Virtualization (SEV) command support")
Cc: <stable@vger.kernel.org> # 4.16.x-
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Brijesh Singh <brijesh.singh@amd.com>
Acked-by: Gary R Hook <gary.hook@amd.com>
Acked-by: Gary R Hook <gary.hook@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/ccp/psp-dev.c

@@ -84,8 +84,6 @@ static irqreturn_t psp_irq_handler(int irq, void *data)
 
 static void sev_wait_cmd_ioc(struct psp_device *psp, unsigned int *reg)
 {
-	psp->sev_int_rcvd = 0;
-
 	wait_event(psp->sev_int_queue, psp->sev_int_rcvd);
 	*reg = ioread32(psp->io_regs + PSP_CMDRESP);
 }
@@ -148,6 +146,8 @@ static int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret)
 	iowrite32(phys_lsb, psp->io_regs + PSP_CMDBUFF_ADDR_LO);
 	iowrite32(phys_msb, psp->io_regs + PSP_CMDBUFF_ADDR_HI);
 
+	psp->sev_int_rcvd = 0;
+
 	reg = cmd;
 	reg <<= PSP_CMDRESP_CMD_SHIFT;
 	reg |= PSP_CMDRESP_IOC;