Re: [PATCH v12 19/37] x86/fred: Update MSR_IA32_FRED_RSP0 during task switch

H. Peter Anvin
2023-11-13T18:45:05Z

On November 13, 2023 1:29:47 PM EST, Borislav Petkov <bp@alien8.de> wrote:
>On Mon, Nov 13, 2023 at 12:36:04PM -0500, H. Peter Anvin wrote:
>> A resource cannot be consumed after the value has been written; this
>> is the only necessary level of serialization, equivalent to, say, RAX.
>
>Lemme see if I understand this correctly using this context as an
>example: after this MSR_IA32_FRED_RSP0 write, any FRED events determined
>to be delivered to level 0 will use this new task stack ptr?
>
>And since the new task is not running yet and the old one isn't running
>either, we're fine here. So the "serialization point" I was talking
>about above is bollocks.
>
>Close? :)
>
>> A serializing instruction stops the entire pipeline until everything
>> has retired and any stores have become globally visible.
>
>Right, we don't need that here.
>
>Thx.
>

Yep!