On Fri, Nov 07, 2025 at 09:59:46AM +0000, Daniel P. Berrangé wrote: > On Fri, Nov 07, 2025 at 02:21:24PM +0530, Naveen N Rao wrote: > > On Thu, Nov 06, 2025 at 01:09:37PM +0100, Markus Armbruster wrote: > > > Pardon my ignorance... > > > > > > "Naveen N Rao (AMD)" <[email protected]> writes: > > > > > > > Add support for configuring the TSC frequency when Secure TSC is enabled > > > > in SEV-SNP guests through a new "tsc-frequency" property on SEV-SNP > > > > guest objects, similar to the vCPU-specific property used by regular > > > > guests and TDX. > > > > > > Which property exactly? > > > > Same name: tsc-frequency specified with '-cpu' > > > > > > > > > A new property is needed since SEV-SNP guests require > > > > the TSC frequency to be specified during early SNP_LAUNCH_START command > > > > before any vCPUs are created. > > > > > > Sounds awkward. > > > > > > Do the two properties set the same thing at different times? > > > > Yes. For regular guests, TSC frequency is set using a vCPU ioctl. > > However, TDX and SEV-SNP (with Secure TSC) require the TSC frequency to > > be set as a VM property (there is a VM ioctl for this purpose). > > The '-cpu' arg is global to the VM, so even though the ioctl is per-VCPU, > a single '-cpu ...,tsc-frequency=NNN' argument applies universally to all > the vCPUs in regular guests. > > > This was Tom's question too (see v2): is there any way to re-use > > 'tsc-frequency' specified with '-cpu' for Secure TSC. > > I see no reason why we can't simply use the existing '-cpu tsc-frequency' > value. Fetch the CPU 0 object and query its "tsc-frequency" property, > and just assume all non-0 CPUs have the same tsc-frequency, since we > don't provide a way to set it differently per-CPU IIUC.
I might be missing something obvious, but did you mean using 'qemu_get_cpu(0)' or 'first_cpu' in sev_snp_launch_start()? That doesn't seem to work (both are NULL). Thanks, Naveen
