The PCI-E spec by default only allows 256MB per memory or IO region for a PCI-E device, one of those regions is also VRAM. There is a way to resize it to the full size of VRAM but it requires 2 features to work properly, PCI-E BAR resizing and Above 4GB Decoding. Windows and Linux have mechanisms for this already but it is not used automatically, AMD seems to be working towards enabling this out-of-the-box on their platforms Due to the feature support requirements, they are only on 500 series + Zen 3 for now, but really anything made in the past maybe 7-8 years supports this.
500+Zen 3 support only is merely to start with, I was told even Intel CPU support is not ruled out for the future. Besides depending on how AMD standardize this, NVIDIA could very easily enable it too. You can already get it to enable on Linux on practically any CPU and GPU, but it requires some fiddling around.
Quelle:
Nemez @ Twitter 3. November am 2020 (inkl. vorstehender & nachstehender Tweets desselben Tweet-Threads)