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

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Message-ID: <20240402224222.vxaqenqvyi32zleb@amd.com>
Date: Tue, 2 Apr 2024 17:42:22 -0500
From: Michael Roth <michael.roth@....com>
To: "Kalra, Ashish" <ashish.kalra@....com>
CC: Tom Lendacky <thomas.lendacky@....com>,
	<linux-tip-commits@...r.kernel.org>, <bp@...en8.de>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/sev: Apply RMP table fixups for kexec.

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@....com>
> > > 
> > > 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@....com>
> > > ---
> > >   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().

-Mike

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