Re: Save a WRMSR GS.base?

[Borislav Petkov]

On Sun, Jun 07, 2026 at 11:46:34PM -0700, H. Peter Anvin wrote:
> WRxSBASE does a 64-bit write,

When REX.W.

The SDM text is confusing:

"If no REX.W prefix is used, the operand size is 32 bits; the upper 32 bits of
the source register are ignored and upper 32 bits of the base address (for FS
or GS) are cleared."

Does this last part that GS is cleared, refer to when WRGSBASE is used with no
REX.W or in general?

> but for GS it would incorrectly address the kernel GS.base.

What does that mean?

Thx.

-- 
Regards/Gruss,
    Boris.

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