Re: [PATCH] x86/sev: Apply RMP table fixups for kexec.

[Kalra, Ashish]

On 4/2/2024 5:42 PM, Michael Roth wrote:
> On Tue, Apr 02, 2024 at 05:31:09PM -0500, Kalra, Ashish wrote:
> > On 4/2/2024 5:09 PM, Tom Lendacky wrote:
> > > On 3/12/24 13:47, Ashish Kalra wrote:
> > > > From: Ashish Kalra <ashish.kalra@xxxxxxx>
> > > >
> > > > RMP table start and end physical range may not be aligned to 2MB in
> > > > the e820 tables causing fatal RMP page faults during kexec boot when
> > > > new page allocations are done in the same 2MB page as the RMP table.
> > > > Check if RMP table start and end physical range in e820_table is not
> > > > aligned to 2MB and in that case use e820__range_update() to map this
> > > > range to reserved.
> > > >
> > > > Override e820__memory_setup_default() to check and apply these RMP table
> > > > fixups in e820_table before e820_table is used to setup
> > > > e280_table_firmware and e820_table_kexec.
> > > >
> > > > Fixes: c3b86e61b756 ("x86/cpufeatures: Enable/unmask SEV-SNP CPU
> > > > feature")
> > > > Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> > > > ---
> > > >    arch/x86/virt/svm/sev.c | 52 +++++++++++++++++++++++++++++++++++++++++
> > > >    1 file changed, 52 insertions(+)
> > > >
> > > > diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
> > > > index cffe1157a90a..e0d7584df28f 100644
> > > > --- a/arch/x86/virt/svm/sev.c
> > > > +++ b/arch/x86/virt/svm/sev.c
> > > > @@ -65,6 +65,8 @@ static u64 probed_rmp_base, probed_rmp_size;
> > > >    static struct rmpentry *rmptable __ro_after_init;
> > > >    static u64 rmptable_max_pfn __ro_after_init;
> > > >    +static char *__init snp_rmptable_e820_fixup(void);
> > > > +
> > > >    static LIST_HEAD(snp_leaked_pages_list);
> > > >    static DEFINE_SPINLOCK(snp_leaked_pages_list_lock);
> > > >    @@ -160,9 +162,59 @@ bool snp_probe_rmptable_info(void)
> > > >        pr_info("RMP table physical range [0x%016llx - 0x%016llx]\n",
> > > >            probed_rmp_base, probed_rmp_base + probed_rmp_size - 1);
> > > >    +    /*
> > > > +     * Override e820__memory_setup_default() to do any RMP table fixups
> > > > +     * for kexec if required.
> > > > +     */
> > > > +    x86_init.resources.memory_setup = snp_rmptable_e820_fixup;
> > > This produces a build warning:
> > >
> > > WARNING: modpost: vmlinux: section mismatch in reference:
> > > snp_probe_rmptable_info+0x95 (section: .text) -> x86_init (section:
> > > .init.data)
> > > WARNING: modpost: vmlinux: section mismatch in reference:
> > > snp_probe_rmptable_info+0x99 (section: .text) -> snp_rmptable_e820_fixup
> > > (section: .init.text)
> > Oh, so this requires snp_probe_rmptable_info() to be fixed to use the __init
> > macro.
> >
> > I believe that snp_probe_rmptable_info() should be anyway using the __init
> > macro and this fix for snp_probe_rmptable_info() needs to be sent as a
> > separate patch and regardless of this patch getting merged or not.
> I think you'll hit issues with:
>
>    bsp_determine_snp() ->           //non-__init
>      snp_probe_rmptable_info()      //__init
>
> and bsp_determine_snp() sticks around as a function pointer assigned to
> cpuinfo_x86 so I don't think you can use __init there.
>
> So might need to just drop __init from snp_rmptable_e820_fixup().

Actually, that will not help as snp_probe_rmptable_info() is *also* 
accessing x86_init.resources.memory_setup

Thanks, Ashish

> > Thanks, Ashish
> >
> > > Thanks,
> > > Tom
> > >
> > > > +
> > > >        return true;
> > > >    }