Re: [PATCH] tools/libs/guest: fix save and restore of pv domains after 32-bit de-support

From: Juergen Gross <jgross@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
	xen-devel@lists.xenproject.org
Cc: Ian Jackson <iwj@xenproject.org>, Wei Liu <wl@xen.org>
Subject: Re: [PATCH] tools/libs/guest: fix save and restore of pv domains after 32-bit de-support
Date: Mon, 7 Jun 2021 13:20:37 +0200	[thread overview]
Message-ID: <747ef58e-3b39-89b5-c48d-37313e33c260@suse.com> (raw)
In-Reply-To: <cd954aa7-ee43-1126-f97a-21c213ef053b@citrix.com>

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On 07.06.21 13:01, Andrew Cooper wrote:
> On 07/06/2021 10:04, Juergen Gross wrote:
>> After 32-bit PV-guests have been security de-supported when not running
>> under PV-shim, the hypervisor will no longer be configured to support
>> those domains per default when not being built as PV-shim.
>>
>> Unfortunately libxenguest will fail saving or restoring a PV domain
>> due to this restriction, as it is trying to get the compat MFN list
>> even for 64 bit guests.
>>
>> Fix that by obtaining the compat MFN list only for 32-bit PV guests.
>>
>> Fixes: 1a0f2fe2297d122a08fe ("SUPPORT.md: Un-shimmed 32-bit PV guests are no longer supported")
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>> ---
>>   tools/libs/guest/xg_sr_common_x86_pv.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/tools/libs/guest/xg_sr_common_x86_pv.c b/tools/libs/guest/xg_sr_common_x86_pv.c
>> index cd33406aab..ad20461e2e 100644
>> --- a/tools/libs/guest/xg_sr_common_x86_pv.c
>> +++ b/tools/libs/guest/xg_sr_common_x86_pv.c
>> @@ -154,6 +154,7 @@ int x86_pv_map_m2p(struct xc_sr_context *ctx)
>>       ctx->x86.pv.compat_m2p_mfn0 = entries[0].mfn;
>>   #else
>>       /* 64 bit toolstacks need to ask Xen specially for it */
>> +    if ( ctx->x86.pv.levels == 3 )
>>       {
>>           struct xen_machphys_mfn_list xmml = {
>>               .max_extents = 1,
> 
> This wants to encompass the whole ifdef block, to avoid having differing
> behaviour between compile widths.
> 
> Also the comment next to compat_m2p_mfn0 wants adjusting to say "only
> set for 32bit PV guests".

Okay, together with Jan's suggestion this makes sense.

Juergen

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