Re: [PATCH v2 2/5] x86/kexec: do unconditional WBINVD in relocate_kernel()

[Huang, Kai]

On 20/03/2024 3:38 am, Tom Lendacky wrote:
> On 3/19/24 06:13, Kirill A. Shutemov wrote:
> > On Tue, Mar 19, 2024 at 01:48:45AM +0000, Kai Huang wrote:
> > > Both SME and TDX can leave caches in incoherent state due to memory
> > > encryption.  During kexec, the caches must be flushed before jumping to
> > > the second kernel to avoid silent memory corruption to the second 
> > > kernel.
> > >
> > > During kexec, the WBINVD in stop_this_cpu() flushes caches for all
> > > remote cpus when they are being stopped.  For SME, the WBINVD in
> > > relocate_kernel() flushes the cache for the last running cpu (which is
> > > executing the kexec).
> > >
> > > Similarly, for TDX after stopping all remote cpus with cache flushed, to
> > > support kexec, the kernel needs to flush cache for the last running cpu.
> > >
> > > Make the WBINVD in the relocate_kernel() unconditional to cover both SME
> > > and TDX.
> >
> > Nope. It breaks TDX guest. WBINVD triggers #VE for TDX guests.
>
> Ditto for SEV-ES/SEV-SNP, a #VC is generated and crashes the guest.

Oh I forgot these.

Hi Kirill,

Then I think patch 1 will also break TDX guest after your series to 
enable multiple cpus for the second kernel after kexec()?

Hi Tom,

I am not aware of kexec() support status for SEV-ES/SEV-SNP guests. 
Does patch 1 break them?