The backport dropped the hunk deleting the setup_clear_cpu_cap() for HLE/RTM,
but retained the hunk adding setup_force_cpu_cap().

Calling both force and clear on the same feature elicits an error, and clear
takes precedence, which breaks the part of the bufix which makes migration
from older versions of Xen function safely for VMs using TSX.

Fixes: f17d848c4caa ("x86/cpuid: Rework HLE and RTM handling")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
---
 xen/arch/x86/spec_ctrl.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index 33343062a7b6..1cfd02d7d7cf 100644
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -1150,9 +1150,6 @@ void __init init_speculation_mitigations(void)
          ((hw_smt_enabled && opt_smt) ||
           !boot_cpu_has(X86_FEATURE_SC_VERW_IDLE)) )
     {
-        setup_clear_cpu_cap(X86_FEATURE_HLE);
-        setup_clear_cpu_cap(X86_FEATURE_RTM);
-
         opt_tsx = 0;
         tsx_init();
     }
-- 
2.11.0

On 15.07.2021 17:10, Andrew Cooper wrote:
> The backport dropped the hunk deleting the setup_clear_cpu_cap() for HLE/RTM,
> but retained the hunk adding setup_force_cpu_cap().
> 
> Calling both force and clear on the same feature elicits an error, and clear
> takes precedence,

Right, I particularly didn't pay attention to this interaction
aspect.

> which breaks the part of the bufix which makes migration
> from older versions of Xen function safely for VMs using TSX.
> 
> Fixes: f17d848c4caa ("x86/cpuid: Rework HLE and RTM handling")
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Acked-by: Jan Beulich <jbeulich@suse.com>

Are you going to put this in, or should I?

Jan

On 15/07/2021 16:39, Jan Beulich wrote:
> On 15.07.2021 17:10, Andrew Cooper wrote:
>> The backport dropped the hunk deleting the setup_clear_cpu_cap() for HLE/RTM,
>> but retained the hunk adding setup_force_cpu_cap().
>>
>> Calling both force and clear on the same feature elicits an error, and clear
>> takes precedence,
> Right, I particularly didn't pay attention to this interaction
> aspect.
>
>> which breaks the part of the bufix which makes migration
>> from older versions of Xen function safely for VMs using TSX.
>>
>> Fixes: f17d848c4caa ("x86/cpuid: Rework HLE and RTM handling")
>> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> Acked-by: Jan Beulich <jbeulich@suse.com>

Thanks.

> Are you going to put this in, or should I?

Feel free to.

~Andrew