Re: [PATCH 1/2] x86/PCI: Disable enhanced atomics on some AMD PCIe ports

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Sep 08, 2026 at 12:00:34PM -0500, Mario Limonciello wrote:
> There have been multiple reports of data corruption that can occur
> with 64-bit DMA when the IOMMU is enabled. This occurs due to some
> BIOSes enabling enhanced atomic operations on PCIe ports.
> 
> When enhanced atomic operations are enabled on PCIe ports for some
> models, data corruption occurs when the 32-bit IOVA space is exhausted.
> The problem is reported on storage devices, but can affect any device
> that uses 64 bit DMA.

I assume this means there's an erratum where NBIO doesn't handle
64-bit DMA correctly when some AMD-specific "enhanced atomics" are
enabled?

Nothing to do with the atomic operations defined by the PCI specs?

> Disable enhanced atomics using SMN for NBIO 7.7 and 7.11 based models.
> 
> Cc: david.laight.linux@gmail.com
> Cc: John Smith <imjohnsmith4000@gmail.com>
> Cc: Lennert Buytenhek <kernel@wantstofly.org>
> Cc: Niklas Cassel <cassel@kernel.org>
> Cc: Roland Waltersson <roland.waltersson@netinsight.net>
> Reported-by: Mikael Etienne <mikael1022bzh@gmail.com>
> Closes: https://lore.kernel.org/all/178789300872.392066.15963676631650361573@gmail.com/
> Reported-by: Arthur Husband <artmoty@gmail.com>
> Closes: https://lore.kernel.org/linux-ide/20260406222335.379935-1-artmoty@gmail.com/
> Reported-by: Alvin Lim <alvinwylim@gmail.com>
> Closes: https://lore.kernel.org/linux-ide/20260621100844.1224301-1-alvinwylim@gmail.com/
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> ---
>  arch/x86/pci/fixup.c | 93 ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 93 insertions(+)
> 
> diff --git a/arch/x86/pci/fixup.c b/arch/x86/pci/fixup.c
> index b301c6c8df753..0857fd9365ec2 100644
> --- a/arch/x86/pci/fixup.c
> +++ b/arch/x86/pci/fixup.c
> @@ -886,6 +886,99 @@ static void quirk_clear_strap_no_soft_reset_dev2_f0(struct pci_dev *dev)
>  	}
>  }
>  DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_AMD, 0x15b8, quirk_clear_strap_no_soft_reset_dev2_f0);
> +
> +/*
> + * Enhanced atomic operations can cause corruption with 64-bit IOVA
> + * on these devices.
> + */
> +#define RX_ENH_ATOMIC_EN		BIT(8)
> +
> +static const u32 nbio_7_7_pcie_smn_addrs[] = {
> +	0x111401d0,
> +	0x111411d0,
> +	0x111421d0,
> +	0x111431d0,
> +	0x111441d0,
> +	0x112401d0,
> +	0x112411d0,
> +	0x112421d0,
> +	0x112431d0,
> +	0x112441d0,
> +	0x112451d0,
> +	0x113401d0,
> +	0x114401d0,
> +};
> +
> +static const u32 nbio_7_11_pcie_smn_addrs[] = {
> +	0x112401d0,
> +	0x112411d0,
> +	0x112421d0,
> +	0x112431d0,
> +	0x112441d0,
> +	0x112451d0,
> +	0x113401d0,
> +	0x113411d0,
> +	0x113421d0,
> +	0x113431d0,
> +	0x113441d0,
> +	0x113451d0,
> +};
> +
> +static void quirk_amd_nbio_enhanced_atomic(struct pci_dev *host_bridge,
> +					   const u32 *smn_addrs,
> +					   size_t nr_smn_addrs)
> +{
> +	bool changed = false;
> +	size_t i;
> +	u32 data;
> +	int ret;
> +
> +	for (i = 0; i < nr_smn_addrs; i++) {
> +		ret = amd_smn_read(0, smn_addrs[i], &data);
> +		if (ret)
> +			continue;
> +		if (!(data & RX_ENH_ATOMIC_EN))
> +			continue;
> +		data = data & ~RX_ENH_ATOMIC_EN;
> +		ret = amd_smn_write(0, smn_addrs[i], data);
> +		if (ret)
> +			continue;
> +		if (changed)
> +			continue;
> +		ret = amd_smn_read(0, smn_addrs[i], &data);
> +		if (ret)
> +			continue;
> +		if (data & RX_ENH_ATOMIC_EN)
> +			continue;
> +		changed = true;
> +	}
> +
> +	if (changed)
> +		pci_info(host_bridge, "enhanced atomics disabled\n");
> +}
> +
> +static void quirk_amd_nbio_7_7_disable_enhanced_atomic(struct pci_dev *dev)
> +{
> +	quirk_amd_nbio_enhanced_atomic(dev, nbio_7_7_pcie_smn_addrs,
> +				       ARRAY_SIZE(nbio_7_7_pcie_smn_addrs));
> +}
> +
> +static void quirk_amd_nbio_7_11_disable_enhanced_atomic(struct pci_dev *dev)
> +{
> +	quirk_amd_nbio_enhanced_atomic(dev, nbio_7_11_pcie_smn_addrs,
> +				       ARRAY_SIZE(nbio_7_11_pcie_smn_addrs));
> +}
> +
> +/* Phoenix, Hawk Point (NBIO 7.7) */
> +DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_AMD, 0x14E8,
> +			quirk_amd_nbio_7_7_disable_enhanced_atomic);
> +
> +/* Strix, Krackan, Strix Halo (NBIO 7.11) */
> +DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_AMD, 0x1507,
> +			quirk_amd_nbio_7_11_disable_enhanced_atomic);
> +DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_AMD, 0x1122,
> +			quirk_amd_nbio_7_11_disable_enhanced_atomic);
> +
>  #endif
>  
>  /*
> -- 
> 2.43.0
>