Original email: From: Tamas K Lengyel <[email protected]> Sent: Wednesday, November 24, 2021 21:12 To: Untitled YAN <[email protected]> Cc: Jan Beulich <[email protected]>; Alexandru Isaila <[email protected]>; Petre Pircalabu <[email protected]>; Xen-devel <[email protected]> Subject: Re: About support for memory event on AMD CPUs > Altp2m is only available on Intel, mem_access (restricting permissions) is > only available on Intel and ARM. No technical reason for it not working on > AMD, it just hasn't been implemented in Xen. > > Tamas > > On Wed, Nov 24, 2021, 4:44 AM Untitled YAN <[email protected]> wrote: > 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].> org> > 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
Dear Tamas, Thanks for your clear answer. So I will watch the update note, or maybe I will try to get an Intel machine for my experiments. Thanks! Untitled YAN
