linux-kernel - Re: [PATCH v2] soc: qcom: cmd-db: Map shared memory as WC, not WB

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Message-ID: <d17e7e6d-12dd-475d-80ae-fa48178d6cf2@linaro.org>
Date: Thu, 18 Jul 2024 09:41:34 +0200
From: Caleb Connolly <caleb.connolly@...aro.org>
To: Maulik Shah <quic_mkshah@...cinc.com>,
 Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konrad.dybcio@...aro.org>
Cc: stephan@...hold.net, swboyd@...omium.org, dianders@...omium.org,
 robdclark@...il.com, nikita@...n.ru, quic_eberman@...cinc.com,
 quic_pkondeti@...cinc.com, quic_lsrao@...cinc.com,
 linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Volodymyr Babchuk <Volodymyr_Babchuk@...m.com>, stable@...r.kernel.org
Subject: Re: [PATCH v2] soc: qcom: cmd-db: Map shared memory as WC, not WB



On 18/07/2024 08:03, Maulik Shah wrote:
> From: Volodymyr Babchuk <Volodymyr_Babchuk@...m.com>
> 
> Linux does not write into cmd-db region. This region of memory is write
> protected by XPU. XPU may sometime falsely detect clean cache eviction
> as "write" into the write protected region leading to secure interrupt
> which causes an endless loop somewhere in Trust Zone.
> 
> The only reason it is working right now is because Qualcomm Hypervisor
> maps the same region as Non-Cacheable memory in Stage 2 translation
> tables. The issue manifests if we want to use another hypervisor (like
> Xen or KVM), which does not know anything about those specific mappings.
> 
> Changing the mapping of cmd-db memory from MEMREMAP_WB to MEMREMAP_WT/WC
> removes dependency on correct mappings in Stage 2 tables. This patch
> fixes the issue by updating the mapping to MEMREMAP_WC.
> 
> I tested this on SA8155P with Xen.
> 
> Fixes: 312416d9171a ("drivers: qcom: add command DB driver")
> Cc: stable@...r.kernel.org # 5.4+
> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@...m.com>
> Tested-by: Nikita Travkin <nikita@...n.ru> # sc7180 WoA in EL2
> Signed-off-by: Maulik Shah <quic_mkshah@...cinc.com>

Reviewed-by: Caleb Connolly <caleb.connolly@...aro.org>
> ---
> Changes in v2:
>   - Use MEMREMAP_WC instead of MEMREMAP_WT
>   - Update commit message from comments in v1
>   - Add Fixes tag and Cc to stable
>   - Link to v1: https://lore.kernel.org/lkml/20240327200917.2576034-1-volodymyr_babchuk@epam.com
> ---
>   drivers/soc/qcom/cmd-db.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/soc/qcom/cmd-db.c b/drivers/soc/qcom/cmd-db.c
> index d84572662017..ae66c2623d25 100644
> --- a/drivers/soc/qcom/cmd-db.c
> +++ b/drivers/soc/qcom/cmd-db.c
> @@ -349,7 +349,7 @@ static int cmd_db_dev_probe(struct platform_device *pdev)
>   		return -EINVAL;
>   	}
>   
> -	cmd_db_header = memremap(rmem->base, rmem->size, MEMREMAP_WB);
> +	cmd_db_header = memremap(rmem->base, rmem->size, MEMREMAP_WC);
>   	if (!cmd_db_header) {
>   		ret = -ENOMEM;
>   		cmd_db_header = NULL;
> 
> ---
> base-commit: 797012914d2d031430268fe512af0ccd7d8e46ef
> change-id: 20240718-cmd_db_uncached-e896da5c5296
> 
> Best regards,

-- 
// Caleb (they/them)