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Re: [PATCH v2 14/16] x86/fsgsbase: Split out __{rd,wr}gskern() helpers
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 19 Aug 2025 15:01:01 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 19 Aug 2025 13:01:10 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 15.08.2025 22:41, Andrew Cooper wrote:
> Right now they're inline in {read,write}_gs_shadow(), but we're going to need
> to use these elsewhere to support FRED.
But why "kern"? We're not dealing with GS in kernel / user terms, but in
real / shadow ones. I'm also not quite happy with the double leading
underscores, fwiw.
As to using them elsewhere to support FRED: How can we when they use SWAPGS,
which isn't available under FRED?
> --- a/xen/arch/x86/include/asm/fsgsbase.h
> +++ b/xen/arch/x86/include/asm/fsgsbase.h
> @@ -32,6 +32,17 @@ static inline unsigned long __rdgsbase(void)
> return base;
> }
>
> +static inline unsigned long __rdgskern(void)
> +{
> + unsigned long base;
> +
> + asm_inline volatile ( "swapgs\n\t"
> + "rdgsbase %0\n\t"
> + "swapgs" : "=r" (base) );
Again strictly speaking "=&r", if already you open-code rdgsbase() now.
Jan
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