{"id":100275,"date":"2018-11-20T07:00:00","date_gmt":"2018-11-20T22:00:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/oldnewthing\/?p=100275"},"modified":"2019-03-13T00:14:25","modified_gmt":"2019-03-13T07:14:25","slug":"20181120-00","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20181120-00\/?p=100275","title":{"rendered":"For a brief period, the kernel tried to deal with gamma rays corrupting the processor cache"},"content":{"rendered":"<p>At one point, the following code was added to the part of the kernel that brings the system out of a low-power state: <\/p>\n<pre>\n        ;\n        ; Invalidate the processor cache so that any stray gamma\n        ; rays (I'm serious) that may have flipped cache bits\n        ; while in <a HREF=\"https:\/\/en.wikipedia.org\/wiki\/Advanced_Configuration_and_Power_Interface\">S1<\/a> will be ignored.\n        ;\n        ; Honestly.  The processor manufacturer asked for this.\n        ; I'm serious.\n        ;\n         invd\n<\/pre>\n<p>I&#8217;m not sure what the thinking here is. I mean, if the cache might have been zapped by a stray gamma ray, then couldn&#8217;t RAM have been zapped by a stray gamma ray, too? Or is processor cache more susceptible to gamma rays than RAM? The person who wrote the comment seems to share my incredulity. <\/p>\n<p>Less than three weeks later, the <code>INVD<\/code> instruction was commented out. But the comment block remains. <\/p>\n<p>In case we decide to resume trying to deal with gamma rays corrupting the the processor cache, I guess. <\/p>\n<p><b>Bonus chatter<\/b>: One of my colleagues wasn&#8217;t part of this specific change, but recalled that these sorts of strange-sounding requests were not uncommon, especially for early processor steppings. The workaround was removed once the problem was fixed in microcode or in a later processor stepping. <\/p>\n","protected":false},"excerpt":{"rendered":"<p>Not sure what good it does.<\/p>\n","protected":false},"author":1069,"featured_media":111744,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[2],"class_list":["post-100275","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-history"],"acf":[],"blog_post_summary":"<p>Not sure what good it does.<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/100275","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/users\/1069"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/comments?post=100275"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/100275\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media\/111744"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media?parent=100275"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=100275"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=100275"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}