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SubjectRe: [PATCH v2 3/3] paravirt: rename paravirt_enabled to paravirt_legacy
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On 02/06/2016 03:59 AM, Luis R. Rodriguez wrote:
> The enumeration of legacy crap by ACPI boot flags seems to provide enough
> details to suit our needs if we really wanted to zero down on the specifics of
> what paravirt_legacy() means, there are these flags:
>
> /* Masks for FADT IA-PC Boot Architecture Flags (boot_flags) [Vx]=Introduced in this FADT revision */
> #define ACPI_FADT_LEGACY_DEVICES (1) /* 00: [V2] System has LPC or ISA bus devices */
> #define ACPI_FADT_8042 (1<<1) /* 01: [V3] System has an 8042 controller on port 60/64 */
> #define ACPI_FADT_NO_VGA (1<<2) /* 02: [V4] It is not safe to probe for VGA hardware */
> #define ACPI_FADT_NO_MSI (1<<3) /* 03: [V4] Message Signaled Interrupts (MSI) must not be enabled */
> #define ACPI_FADT_NO_ASPM (1<<4) /* 04: [V4] PCIe ASPM control must not be enabled */
> #define ACPI_FADT_NO_CMOS_RTC (1<<5) /* 05: [V5] No CMOS real-time clock present */
>
> I checked and I didn't see qemu using any of the ACPI boot flags,
> but I suspected qemu instances must use a series of legacy crap.
> Likewise for KVM.
>
> coreboot defines legacy free when you don't have any of the above flags set:
> #define ACPI_FADT_LEGACY_FREE 0x00 /* No legacy devices (including 8042) *
>
> Would it be sufficient to just stick to "pv legacy" equivalent
> of requiring just ACPI_FADT_LEGACY_DEVICES and ACPI_FADT_8042 ?

I believe unprivileged PV guests may be compiled without CONFIG_ACPI if
you are talking about requiring (or manually setting) these flags.

-boris

>
> I should point out It turns out ACPI_FADT_NO_CMOS_RTC matches lguest's and it
> seems that's the only reason we have that RTC PV flag and the features pv
> field... with the linker table + x86 subarch use it should be relatively simple
> to remove paravirt_has_feature() paravirt_has() and PV_SUPPORTED_RTC. lguest
> would just be the only subarch that opts out.
>
> Luis

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