Re: [PATCH] platform/x86/dell: add buffer allocation/free functions for SMI calls

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On 18.03.22 16:22, David Laight wrote:
From: Juergen Gross
Sent: 18 March 2022 15:10

The dcdbas driver is used to call SMI handlers for both, dcdbas and
dell-smbios-smm. Both drivers allocate a buffer for communicating
with the SMI handler. The physical buffer address is then passed to
the called SMI handler via %ebx.

Unfortunately this doesn't work when running in Xen dom0, as the
physical address obtained via virt_to_phys() is only a guest physical
address, and not a machine physical address as needed by SMI.

The physical address from virt_to_phy() is always wrong.
That is the physical address the cpu has for the memory.
What you want is the address the dma master interface needs to use.
That can be different for a physical system - no need for virtualisation.

On x86 they do usually match, but anything with a full iommu
will need completely different addresses.

Yes, thanks for reminding me of that.

The SMI handler is running on the cpu, right? So using the DMA
address is wrong in case of an IOMMU. I really need the machine
physical address.


Juergen

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