On Mon, Sep 09, 2019 at 04:51:24PM +0100, Andrew Cooper wrote:
> 7a0 is an integer field, not a mask - taking the logical and of the hardware
> and policy values results in nonsense. Instead, take the policy value
> directly.
>
> Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
> ---
> CC: Jan Beulich <jbeul...@suse.com>
> CC: Wei Liu <w...@xen.org>
> CC: Roger Pau Monné <roger....@citrix.com>
>
> Even Rome hardware has 7[0].eax still as 0, and there is no sensible reason to
> set max_subleaf higher at this point, so this is only a latent bug for now.
> ---
> xen/arch/x86/domctl.c | 13 +++++++++----
> 1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
> index 1e98fc8009..35ad8cb51c 100644
> --- a/xen/arch/x86/domctl.c
> +++ b/xen/arch/x86/domctl.c
> @@ -218,11 +218,16 @@ static int update_domain_cpuid_info(struct domain *d,
> if ( is_pv_domain(d) && ((levelling_caps & LCAP_7ab0) == LCAP_7ab0) )
> {
> uint64_t mask = cpuidmask_defaults._7ab0;
> - uint32_t eax = ctl->eax;
> - uint32_t ebx = p->feat._7b0;
>
> - if ( boot_cpu_data.x86_vendor & (X86_VENDOR_AMD |
> X86_VENDOR_HYGON) )
> - mask &= ((uint64_t)eax << 32) | ebx;
> + /*
> + * Leaf 7[0].eax is max_subleaf, not a feature mask. Take it
> + * wholesale from the policy, but clamp the features in 7[0].ebx
> + * per usual.
> + */
> + if ( boot_cpu_data.x86_vendor &
> + (X86_VENDOR_AMD | X86_VENDOR_HYGON) )
> + mask = (((uint64_t)p->feat.max_subleaf << 32) |
> + ((uint32_t)mask | p->feat._7b0));
Why do you set the high bits of the mask (63:30) with the max subleaf?
According to the document I have bits 63:30 are reserved, and that
seems to match the expected CPUID return value, that lists CPUID
Fn0000_0007_EAX_x0 content as reserved.
Thanks, Roger.
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