Re: [PATCH v5 16/16] x86/tdx: Add cmdline option to force use of ioremap_host_shared

Randy Dunlap
2021-10-09T01:45:49Z

On 10/8/21 5:37 PM, Kuppuswamy Sathyanarayanan wrote:
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 91ba391f9b32..0af19cb1a28c 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2076,6 +2076,18 @@
> 1 - Bypass the IOMMU for DMA.
> unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
>
> + ioremap_force_shared= [X86_64, CCG]
> + Force the kernel to use shared memory mappings which do
> + not use ioremap_host_shared/pcimap_host_shared to opt-in
> + to shared mappings with the host. This feature is mainly
> + used by a confidential guest when enabling new drivers
> + without proper shared memory related changes. Please note
> + that this option might also allow other non explicitly
> + enabled drivers to interact with the host in confidential
> + guest, which could cause other security risks. This option
> + will also cause BIOS data structures to be shared with the
> + host, which might open security holes.

Hi,
This cmdline option text should have a little bit more info. Just as an
example/template:

acpi_apic_instance= [ACPI, IOAPIC]
Format: <int>
2: use 2nd APIC table, if available
1,0: use 1st APIC table
default: 0

So what is expected after the "=" sign?...

thanks.
--
~Randy