AMD Publishes Documentation On RDNA 1.0 ISA

[phoronix]

Phoronix: AMD Publishes Documentation On RDNA 1.0 ISA

AMD has published their instruction set architecture documentation for their new RDNA 1.0 architecture found on their new Radeon RX 5700 series GPUs and other forthcoming products...

http://www.phoronix.com/scan.php?page=news_item&px=AMD-RDNA-1.0-ISA-Docs

[shmerl]

Regarding AMD, but a bit unrelated. Apparently Ryzen 3000 series CPUs have another problem besides RDRAND (RDRAND one was fixed in firmware updates). It's broken SGDT instruction:

https://github.com/ValveSoftware/Proton/issues/2927

Did AMD say anything about that?

[Peter Fodrek]

Regarding AMD, but a bit unrelated. Apparently Ryzen 3000 series CPUs have another problem besides RDRAND (RDRAND one was fixed in firmware updates). It's broken SGDT instruction:

https://github.com/ValveSoftware/Proton/issues/2927

Did AMD say anything about that?

SGDT — Store Global Descriptor Table Register

SGDT is useful only by operating-system software.

However, it can be used in application programs without causing an exception
https://www.felixcloutier.com/x86/sgdt

Why to enable something that is not useful in CPU ring lager then 0? To lower security level of the CPU or not to block not correctly written software form being executed


I know that if you block all not correctly written software your computer became software-less..

[shmerl]

Why [/URL]to enable something that is not useful in CPU ring lager then 0?

Apparently Wine needs it: https://lwn.net/Articles/738209/

[mlau]

SGDT — Store Global Descriptor Table Register

SGDT is useful only by operating-system software.

However, it can be used in application programs without causing an exception
[URL="https://www.felixcloutier.com/x86/sgdt"]https://www.felixcloutier.com/x86/sgdt

You left out the most interesting part:

[...]without causing an exception to be generated if CR4.UMIP = 0.

Does Ryzen 3xxx support UMIP? Then this can be resolved by building a kernel without UMIP support.

[shmerl]

Does Ryzen 3xxx support UMIP? Then this can be resolved by building a kernel without UMIP support.

Apparently Wine worked fine with Zen+, so I doubt Zen 2 is supposed to drop stuff that worked before. What's the way to check if UIMP is supported, is there some flag in cpuinfo?

[dungeon]

Does Ryzen 3xxx support UMIP? Then this can be resolved by building a kernel without UMIP support.

Looks like Zen 2 supports it, since it seems properly prevents SGDT instruction to be used.

On the other hand i guess some people like to be able to run everything, even viruses Probably UMIP should be build as module, for ease switch off for these who really does not care.

BTW, i don't have a hardware, just looks like it might be a feature or a bug

[mczak]

Looks like Zen 2 supports it, since it seems properly prevents SGDT instruction to be used.

I think UMIP could be disabled via clearcpuid=514 on the boot command line, so sgdt from userspace should no longer crash?
I have no idea if the crash here is legit or not, but it should be noted that Zen 2 is the first widely available cpu which supports this, even though it seems intel specified this extension - cannonlake should support it but doesn't meet the definition of widely available by miles...

[moilami]

Appears RDNA is going to reign in the forthcoming years. Good!

[Lynxeye]

You left out the most interesting part:

[...]without causing an exception to be generated if CR4.UMIP = 0.

Does Ryzen 3xxx support UMIP? Then this can be resolved by building a kernel without UMIP support.

The cover letter of the patchset implementing UMIP even mentions Wine and the kernel parameter (umip=novm86) needed to make it work.