linux-kernel - Re: [RFC PATCH] irqchip/gic-v4.1:fix the kdump GIC ITS RAS error for ITS BASER2

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Date:   Tue, 14 Dec 2021 09:26:08 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Jay Chen <jkchen@...ux.alibaba.com>
Cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org,
        zhangliguang@...ux.alibaba.com,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: Re: [RFC PATCH] irqchip/gic-v4.1:fix the kdump GIC ITS RAS error for ITS BASER2

[+ Lorenzo, just in case...]

Hi Jay,

Thanks for this.

On Tue, 14 Dec 2021 06:47:16 +0000,
Jay Chen <jkchen@...ux.alibaba.com> wrote:
> 
> We encounter a GIC RAS Error in below flow:
> (1) Configure ITS related register (including
> 	GITS_BASER2, GITS_BASER2.valid = 1'b1)
> (2) Configure GICR related register (including
> 	GICR_VPROPBASER, GICR_VPROPBASER.valid = 1'b1)
> The common settings in above 2 register are the same
> and currently everything is OK
> (3) Kernel panic and os start the kdump flow.And then os
> reconfigure ITS related register (including GITS_BASER2,
> GITS_BASER2.valid = 1'b1). But at this time, gicr_vpropbaser
> is not initialized, so it is still an old value. At this point,
> the new value of its_baser2 and the old value of gicr_vpropbaser is
> different, resulting in its RAS error.
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=215327

I'm sorry, but I don't have any access to this. Please add all the
relevant details to the commit message and drop the link.

Could you please detail what HW this is on? The architecture
specification for GICv4.1 doesn't make any mention of RAS error
conditions, so this must be implementation specific. A reference to
the TRM of the IP would certainly help.

Now, I think you have identified something interesting, but I'm not
convinced by the implementation, see below.

> 
> Signed-off-by: Jay Chen <jkchen@...ux.alibaba.com>
> ---
>  drivers/irqchip/irq-gic-v3-its.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index eb0882d15366..c340bbf4427b 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -2623,6 +2623,12 @@ static int its_alloc_tables(struct its_node *its)
>  			return err;
>  		}
>  
> +		if ((i == 2) && is_kdump_kernel() && is_v4_1(its)) {
> +			val = its_read_baser(its, baser);
> +			val &= ~GITS_BASER_VALID;
> +			its_write_baser(its, baser, val);
> +		}

This looks like a very odd way to address the issue. You are silently
disabling the Base Register containing the VPE table, and carry on as
if nothing happened. What happen if someone starts a guest using
direct injection at this point? A kdump kernel still is a full fledged
kernel, and I don't expect it to behave differently.

If we are to make this work, we need to either disable the v4.1
extension altogether or sanitise the offending registers so that we
don't leave things in a bad state. My preference is of course the
latter.

Could you please give this patch a go and let me know if it helps?

Thanks,

	M.

diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index daec3309b014..cb339ace5046 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -920,6 +920,15 @@ static int __gic_update_rdist_properties(struct redist_region *region,
 {
 	u64 typer = gic_read_typer(ptr + GICR_TYPER);

+	/* Boot-time cleanup */
+	if ((typer & GICR_TYPER_VLPIS) && (typer & GICR_TYPER_RVPEID)) {
+		u64 val;
+
+		val = gicr_read_vpropbaser(ptr + SZ_128K + GICR_VPROPBASER);
+		val &= ~GICR_VPROPBASER_4_1_VALID;
+		gicr_write_vpropbaser(val, ptr + SZ_128K + GICR_VPROPBASER);
+	}
+
 	gic_data.rdists.has_vlpis &= !!(typer & GICR_TYPER_VLPIS);

 	/* RVPEID implies some form of DirectLPI, no matter what the doc says... :-/ */

-- 
Without deviation from the norm, progress is not possible.