Messages in this thread |  | | Subject | Re: [PATCH RFC 3/7] kvm: x86: XSAVE state and XFD MSRs context switch | From | "Liu, Jing2" <> | Date | Mon, 22 Feb 2021 16:51:46 +0800 |
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On 2/9/2021 2:55 AM, Konrad Rzeszutek Wilk wrote: > On Mon, Feb 08, 2021 at 07:12:22PM +0100, Paolo Bonzini wrote: [...] >> >> However, running the host with _more_ bits set than necessary in XFD should >> not be a problem as long as the host doesn't use the AMX instructions. So >> perhaps Jing can look into keeping XFD=0 for as little time as possible, and >> XFD=host_XFD|guest_XFD as much as possible. > This sounds like the lazy-fpu (eagerfpu?) that used to be part of the > kernel? I recall that we had a CVE for that - so it may also be worth > double-checking that we don't reintroduce that one. Not sure if this means lazy restore, but the spec mentions that "System software should not use XFD to implement a 'lazy restore' approach to management of the XTILEDATA state component." One reason is XSAVE(S) will lose the xTILEDATA when XFD[i] is nonzero.
Thanks, Jing
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