Messages in this thread | | | Date | Mon, 28 Jul 2014 17:39:55 -0300 | From | Eduardo Habkost <> | Subject | Re: [PATCH] x86, paravirt: BUG_ON on {rd,wr}msr exceptions |
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On Mon, Jul 28, 2014 at 12:18:10PM -0700, H. Peter Anvin wrote: > On 07/28/2014 12:04 PM, Eduardo Habkost wrote: > > When CONFIG_PARAVIRT is enabled, the kernel is ignoring exceptions on > > the {rd,wr}msr instructions. This makes serious issues (either on the > > guest kernel, or on the host) be silently ignored, and is different from > > the native MSR code (which does not ignore the exceptions). > > > > As paravirt.h already includes linux/bug.h, I don't see what was the > > original issue preventing BUG_ON from being used. > > > > Change rdmsr(), wrmsr(), and rdmsrl() to BUG_ON() on errors. > > How much does this bloat the kernel?
It seems to add 8 bytes to each {wr,rd}msr() call (4 extra instructions: test, jmp, ud2, jmp).
allyesconfig, paravirt enabled, before:
text data bss dec hex filename 108368312 23500872 55705600 187574784 b2e2a00 vmlinux
allyesconfig, paravirt enabled, after:
text data bss dec hex filename 108384438 23500904 55717888 187603230 b2e991e vmlinux
allyesconfig vmlinux is 28446 bytes larger.
An alternative is to add read_msr_unsafe() & write_msr_unsafe() fields to pv_cpu_ops, pointing to native_read_msr() & native_write_msr().
-- Eduardo
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