Re: [PATCH v2] target/i386: Restore TSX features with taa-no

[Paolo Bonzini]

On 7/14/22 07:36, Zhenzhong Duan wrote:
> On ICX-2S2 host, when run L2 guest with both L1/L2 using Icelake-Server-v3
> or above, we got below warning:
>
> "warning: host doesn't support requested feature: MSR(10AH).taa-no [bit 8]"
>
> This is because L1 KVM doesn't expose taa-no to L2 if RTM is disabled,
> then starting L2 qemu triggers the warning.
>
> Fix it by restoring TSX features in Icelake-Server-v3, which may also help
> guest performance if host isn't susceptible to TSX Async Abort (TAA)
> vulnerabilities.
>
> Fixes: d965dc35592d ("target/i386: Add ARCH_CAPABILITIES related bits into 
> Icelake-Server CPU model")
> Tested-by: Xiangfei Ma <xiangfeix.ma@intel.com>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
> ---
> v2: Rewrite commit message

Why wouldn't the fix be (in an Icelake-Server-v4 model) to remove taa-no?

Paolo

>   target/i386/cpu.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 14f681e998cc..25ef972a3eed 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -3423,6 +3423,9 @@ static const X86CPUDefinition builtin_x86_defs[] = {
>               {
>                   .version = 3,
>                   .props = (PropValue[]) {
> +                    /* Restore TSX features removed by -v2 above */
> +                    { "hle", "on" },
> +                    { "rtm", "on" },
>                       { "arch-capabilities", "on" },
>                       { "rdctl-no", "on" },
>                       { "ibrs-all", "on" },