linux-kernel - Re: [PATCH v3 1/1] iommu/vt-d: Serialize IOMMU GCMD register modifications

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Message-ID: <20200904093945.GO6714@8bytes.org>
Date:   Fri, 4 Sep 2020 11:39:45 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: [PATCH v3 1/1] iommu/vt-d: Serialize IOMMU GCMD register
 modifications

On Fri, Aug 28, 2020 at 08:06:15AM +0800, Lu Baolu wrote:
> The VT-d spec requires (10.4.4 Global Command Register, GCMD_REG General
> Description) that:
> 
> If multiple control fields in this register need to be modified, software
> must serialize the modifications through multiple writes to this register.
> 
> However, in irq_remapping.c, modifications of IRE and CFI are done in one
> write. We need to do two separate writes with STS checking after each. It
> also checks the status register before writing command register to avoid
> unnecessary register write.
> 
> Fixes: af8d102f999a4 ("x86/intel/irq_remapping: Clean up x2apic opt-out security warning mess")
> Cc: Andy Lutomirski <luto@...capital.net>
> Cc: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> Cc: Kevin Tian <kevin.tian@...el.com>
> Cc: Ashok Raj <ashok.raj@...el.com>
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
>  drivers/iommu/intel/irq_remapping.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)

Applied for v5.9, thanks.