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Subject: Re: [PATCH] iommu/amd: Fix loop timeout issue in
 iommu_ga_log_enable()
To:     Joerg Roedel <joro@8bytes.org>, <iommu@lists.linux-foundation.org>
CC:     Joerg Roedel <jroedel@suse.de>, <linux-kernel@vger.kernel.org>,
        "Maxim Levitsky" <mlevitsk@redhat.com>,
        Will Deacon <will@kernel.org>
References: <20220131161749.4021-1-joro@8bytes.org>
From:   John Garry <john.garry@huawei.com>
Message-ID: <48a674ae-f5cd-fc06-4505-6d863e6dad69@huawei.com>
Date:   Mon, 31 Jan 2022 17:06:03 +0000
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On 31/01/2022 16:17, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@suse.de>
> 
> The polling loop for the register change in iommu_ga_log_enable() needs
> to have a udelay() in it.  Otherwise the CPU might be faster than the
> IOMMU hardware and wrongly trigger the WARN_ON() further down the code
> stream.
> 
> Fixes: 8bda0cfbdc1a ("iommu/amd: Detect and initialize guest vAPIC log")
> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> ---
>   drivers/iommu/amd/init.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index dc338acf3338..d2e09d53851f 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -834,6 +834,7 @@ static int iommu_ga_log_enable(struct amd_iommu *iommu)
>   		status = readl(iommu->mmio_base + MMIO_STATUS_OFFSET);
>   		if (status & (MMIO_STATUS_GALOG_RUN_MASK))
>   			break;
> +		udelay(1);

Maybe readl_relaxed_poll_timeout_atomic() could be used instead

Thanks,
John

>   	}
>   
>   	if (WARN_ON(i >= LOOP_TIMEOUT))
>