Original email: From: Jan Beulich <[email protected]> Sent: Wednesday, November 24, 2021 17:27 To: Untitled YAN <[email protected]> Cc: [email protected] <[email protected]>; [email protected] <[email protected]>; [email protected] <[email protected]>; [email protected] <[email protected]> Subject: Re: About support for memory event on AMD CPUs > On 24.11.2021 10:23, Untitled YAN wrote: > > Original email: > > > > From: Jan Beulich <[email protected]> > > Sent: Wednesday, November 24, 2021 15:54 > > To: YAN Untitled <[email protected]> > > Cc: [email protected] <[email protected]>; [email protected] > > <[email protected]>; [email protected] > > <[email protected]>; [email protected] > > <[email protected] enproject.>org> > > Subject: Re: About support for memory event on AMD CPUs > > > >> On 23.11.2021 18:14, YAN Untitled wrote: > >>> Dear developers, > >>> > >>> Short version: is memory event supported on AMD CPUs or is it going to be > >>> supported? > >>> > >>> Long version: > >>> > >>> Environment: LibVMI 0.15.0 + Xen 4.14.3 on an **AMD CPU** (5950x), 64-bit > >>> Debian 11 Dom0. > >>> > >>> What I am trying to accomplish: register a **memory event** handler, so > >>> that > >>> I can capture all memory accesses within a specific range issued by any > >>> thread, > >>> or all memory accesses within any range issued by a specific thread. > >>> > >>> What I got instead: an error from LibVMI saying > >>> "xc_hvm_set_mem_access failed with code: -1". > >>> > >>> Some investigation: by inspecting the source code of LibVMI, I find the > >>> direct > >>> cause is one of the libxc functions, 1) xc_set_mem_access or > >>> 2) xc_altp2m_set_mem_access, returned error code -1. > >>> > >>> After some searching, I found someone else having a similar problem [1]. > >>> I also > >>> noted LibVMI says: > >>> > >>>> Currently only the Xen Hypervisor provides these features, > >>>> and some of these are specifically only available on Intel CPUs > >>> > >>> However, I can't find the exact confirmation for the availability of > >>> memory > >>> event on AMD CPUs from https://wiki.xenproject.org. > >> > >> Aiui underlying what you want is altp2m, which presently depends (in > >> the hypervisor) on EPT being available (and in use for the guest in > >> question). > >> > >> Jan > > > > Dear Jan, > > > > Thanks for your reply. I really appreciate the information. After some > > searching with the keyword "EPT" I found [1]. So I checked on dom0 with > > "xl dmesg | grep HAP", which says: > > > >> (XEN) HVM: Hardware Assisted Paging (HAP) detected > >> (XEN) HVM: HAP page sizes: 4kB, 2MB, 1GB > > > > And the guest is an HVM guest running Debian 10 with kernel v4.16 built from > > source. Most of the configuration of the guest is generated by virt-manager. > > The "xl list -l" shows that there is no explicit configuration for EPT, RVI > > or > > HAP, but it does say the "type" is "hvm". > > HAP is the term covering EPT on the Intel side and NPT for AMD. > > Jan
Dear Jan, Yeah that's why I wanted to confirm if the HAP is enabled for the guest - it turns out it is enabled but for some reason, xc_altp2m_set_mem_access failed. I am trying to replicate my setup on an Intel machine to find out if it's a configuration problem. Still don't know if it's implemented for AMD but thanks for your help and information. Untitled YAN
