[PATCH v2 2/2] riscv: T-Head: Test availability bit before enabling MAEE errata

[Conor Dooley]

On Fri, Mar 29, 2024 at 01:14:14PM +0100, Christoph Müllner wrote:
> T-Head's MAEE mechanism (non-compatible equivalent of RVI's Svpbmt)
> is currently assumed for all T-Head harts. However, QEMU recently
> decided to drop acceptance of guests that write reserved bits in PTEs.
> As MAEE uses reserved bits in PTEs and Linux applies the MAEE errata
> for all T-Head harts, this broke the Linux startup on QEMU emulations
> of the C906 emulation.
> 
> This patch attempts to address this issue by testing the MAEE bit
> in the th.sxstatus CSR. This CSR is available in HW and can be
> emulated in QEMU.
> 
> This patch also makes the MAEE probing mechanism reliable, because
> a test for the right combination of mvendorid, marchid, and mimpid
> is not sufficient to enable MAEE.
> 
> Signed-off-by: Christoph Müllner <christoph.muellner at vrull.eu>

Seems ideal to me, I'm guessing the QEMU guys were okay with emulating
the CSR. I don't see any screaming at the very least on the patch for
it.
Reviewed-by: Conor Dooley <conor.dooley at microchip.com>

Thanks,
Conor.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 228 bytes
Desc: not available
URL: <http://lists.infradead.org/pipermail/linux-riscv/attachments/20240404/a1f4e419/attachment.sig>