On 08/22/2014 11:32 AM, Jan Beulich wrote:
On 19.08.14 at 15:25, <jgr...@suse.com> wrote:@@ -118,8 +167,14 @@ void pat_init(void) PAT(4, WB) | PAT(5, WC) | PAT(6, UC_MINUS) | PAT(7, UC);/* Boot CPU check */ - if (!boot_pat_state) + if (!boot_pat_state) { rdmsrl(MSR_IA32_CR_PAT, boot_pat_state); + /* + * Init cache mode tables before writing MSR to give Xen a + * chance to correct the changes when doing the write. + */This comment seems pretty odd to me: For one, a PV guest on Xen shouldn't be trying to write PAT MSR at all under the current ABI (the write will be ignored, yes, but accompanied with a warning message, which PV kernels - by the mere fact that they're PV - should try to avoid). And then "correct the changes" both gives the impression as if they were wrong and as if some of what the kernel writes may be under the kernel's control. Hence I think this code and comment should either be consistently assuming that the kernel has no control at all, or should read back the value after having written it, and set the internal tables based on the value read back.
I think the latter alternative is the better one. I'll change the patch. Juergen -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
