Re: [PATCH] x86/paravirt: Add missing noinstr to arch_local*() helpers

peterz
2020-08-05T19:54:41Z

On Wed, Aug 05, 2020 at 03:59:40PM +0200, Marco Elver wrote:
> On Wed, Aug 05, 2020 at 03:42PM +0200, peterz@infradead.org wrote:

> > Shouldn't we __always_inline those? They're going to be really small.
>
> I can send a v2, and you can choose. For reference, though:
>
> ffffffff86271ee0 <arch_local_save_flags>:
> ffffffff86271ee0: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
> ffffffff86271ee5: 48 83 3d 43 87 e4 01 cmpq $0x0,0x1e48743(%rip) # ffffffff880ba630 <pv_ops+0x120>
> ffffffff86271eec: 00
> ffffffff86271eed: 74 0d je ffffffff86271efc <arch_local_save_flags+0x1c>
> ffffffff86271eef: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
> ffffffff86271ef4: ff 14 25 30 a6 0b 88 callq *0xffffffff880ba630
> ffffffff86271efb: c3 retq
> ffffffff86271efc: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
> ffffffff86271f01: 0f 0b ud2

> ffffffff86271a90 <arch_local_irq_restore>:
> ffffffff86271a90: 53 push %rbx
> ffffffff86271a91: 48 89 fb mov %rdi,%rbx
> ffffffff86271a94: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
> ffffffff86271a99: 48 83 3d 97 8b e4 01 cmpq $0x0,0x1e48b97(%rip) # ffffffff880ba638 <pv_ops+0x128>
> ffffffff86271aa0: 00
> ffffffff86271aa1: 74 11 je ffffffff86271ab4 <arch_local_irq_restore+0x24>
> ffffffff86271aa3: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
> ffffffff86271aa8: 48 89 df mov %rbx,%rdi
> ffffffff86271aab: ff 14 25 38 a6 0b 88 callq *0xffffffff880ba638
> ffffffff86271ab2: 5b pop %rbx
> ffffffff86271ab3: c3 retq
> ffffffff86271ab4: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
> ffffffff86271ab9: 0f 0b ud2

Blergh, that's abysmall. In part I suspect because you have
CONFIG_PARAVIRT_DEBUG, let me try and untangle that PV macro maze.