On Fri, Dec 18, 2020 at 06:13:47PM -0800, Hill Ma wrote:
> This prevents illegal instruction on cpus do not support xgetbv.
>
> Buglink: https://bugs.launchpad.net/qemu/+bug/1758819
> Signed-off-by: Hill Ma <maahiuz...@gmail.com>
> ---
> target/i386/hvf/x86_cpuid.c | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
Hi Hill,
I'm sorry for delay with the review.
> diff --git a/target/i386/hvf/x86_cpuid.c b/target/i386/hvf/x86_cpuid.c
> index a6842912f5..b4b7111fc3 100644
> --- a/target/i386/hvf/x86_cpuid.c
> +++ b/target/i386/hvf/x86_cpuid.c
> @@ -100,11 +100,16 @@ uint32_t hvf_get_supported_cpuid(uint32_t func,
> uint32_t idx,
> break;
> case 0xD:
> if (idx == 0) {
> - uint64_t host_xcr0 = xgetbv(0);
> - uint64_t supp_xcr0 = host_xcr0 & (XSTATE_FP_MASK |
> XSTATE_SSE_MASK |
> + uint64_t supp_xcr0 = XSTATE_FP_MASK | XSTATE_SSE_MASK |
> XSTATE_YMM_MASK | XSTATE_BNDREGS_MASK |
> XSTATE_BNDCSR_MASK | XSTATE_OPMASK_MASK |
> - XSTATE_ZMM_Hi256_MASK |
> XSTATE_Hi16_ZMM_MASK);
> + XSTATE_ZMM_Hi256_MASK |
> XSTATE_Hi16_ZMM_MASK;
> + if ((ecx & CPUID_EXT_AVX) &&
> + (ecx & CPUID_EXT_XSAVE) &&
> + (ecx & CPUID_EXT_OSXSAVE)) {
It's sufficient to check only CPUID_EXT_OSXSAVE to ensure xgetbv
presence (per SDM Vol. 1 13-5):
Software operating with CPL > 0 may need to determine whether the
XSAVE feature set and certain XSAVE-enabled features have been
enabled. If CPL > 0, execution of the MOV from CR4 instruction causes
a general-protection fault (#GP). The following alternative mechanisms
allow software to discover the enabling of the XSAVE feature set
regardless of CPL:
* The value of CR4.OSXSAVE is returned in CPUID.1:ECX.OSXSAVE[bit 27].
If software determines that CPUID.1:ECX.OSXSAVE = 1, the processor
supports the XSAVE feature set and the feature set has been enabled in
CR4.
* Executing the XGETBV instruction with ECX = 0 returns the value of
XCR0 in EDX:EAX. XGETBV can be executed if CR4.OSXSAVE = 1 (if
CPUID.1:ECX.OSXSAVE = 1), regardless of CPL.
> + uint64_t host_xcr0 = xgetbv(0);
> + supp_xcr0 &= host_xcr0;
> + }
> eax &= supp_xcr0;
I think instead of the patch you can do:
- if (idx == 0) {
+ if (idx == 0 && (ecx & CPUID_EXT_OSXSAVE)) {
That'd keep host values returned from CPUID on platforms that don't
support XSAVE.
Thanks,
Roman
> } else if (idx == 1) {
> hv_vmx_read_capability(HV_VMX_CAP_PROCBASED2, &cap);
> --
> 2.20.1 (Apple Git-117)
>
