From: David Laight <David.Laight@ACULAB.COM>
To: 'Xin Li' <xin3.li@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>
Cc: "tglx@linutronix.de" <tglx@linutronix.de>,
"mingo@redhat.com" <mingo@redhat.com>,
"bp@alien8.de" <bp@alien8.de>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
"hpa@zytor.com" <hpa@zytor.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"brgerst@gmail.com" <brgerst@gmail.com>,
"chang.seok.bae@intel.com" <chang.seok.bae@intel.com>
Subject: RE: [PATCH v3 3/6] x86/gsseg: make asm_load_gs_index() take an u16
Date: Fri, 14 Oct 2022 12:28:25 +0000 [thread overview]
Message-ID: <86f60a8edf0e458c86cd84970364cfa2@AcuMS.aculab.com> (raw)
In-Reply-To: <20221013200134.1487-4-xin3.li@intel.com>
From: Xin Li
> Sent: 13 October 2022 21:02
>
> From: "H. Peter Anvin (Intel)" <hpa@zytor.com>
>
> Let gcc know that only the low 16 bits of load_gs_index() argument
> actually matter. It might allow it to create slightly better
> code. However, do not propagate this into the prototypes of functions
> that end up being paravirtualized, to avoid unnecessary changes.
Using u16 will almost always make the code worse.
At some point the value has to be masked and/or extended
to ensure an out of range value doesn't appear in
a register.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2022-10-14 12:28 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-13 20:01 [PATCH v3 0/6] Enable LKGS instruction Xin Li
2022-10-13 20:01 ` [PATCH v3 1/6] x86/cpufeature: add cpu feature bit for LKGS Xin Li
2022-10-13 20:01 ` [PATCH v3 2/6] x86/opcode: add LKGS instruction to x86-opcode-map Xin Li
2022-10-13 20:01 ` [PATCH v3 3/6] x86/gsseg: make asm_load_gs_index() take an u16 Xin Li
2022-10-14 12:28 ` David Laight [this message]
2022-10-15 0:13 ` Li, Xin3
2022-10-15 2:41 ` H. Peter Anvin
2022-10-17 7:49 ` David Laight
2022-10-17 18:39 ` H. Peter Anvin
2022-10-13 20:01 ` [PATCH v3 4/6] x86/gsseg: move local_irq_save/restore() into asm_load_gs_index() Xin Li
2022-10-15 8:51 ` Thomas Gleixner
2022-10-18 17:25 ` Li, Xin3
2022-10-18 18:13 ` H. Peter Anvin
2022-10-18 21:29 ` Li, Xin3
2022-10-13 20:01 ` [PATCH v3 5/6] x86/gsseg: move load_gs_index() to its own header file Xin Li
2022-10-13 20:01 ` [PATCH v3 6/6] x86/gsseg: use the LKGS instruction if available for load_gs_index() Xin Li
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