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Re: [PATCH v2 7/9] x86/svm: VMEntry/Exit logic for MSR_SPEC_CTRL
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 31 Jan 2022 13:55:08 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Mon, 31 Jan 2022 12:55:24 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 28.01.2022 14:29, Andrew Cooper wrote:
> --- a/xen/arch/x86/hvm/svm/entry.S
> +++ b/xen/arch/x86/hvm/svm/entry.S
> @@ -55,11 +55,12 @@ __UNLIKELY_END(nsvm_hap)
> mov %rsp, %rdi
> call svm_vmenter_helper
>
> - mov VCPU_arch_msrs(%rbx), %rax
> - mov VCPUMSR_spec_ctrl_raw(%rax), %eax
> + clgi
>
> /* WARNING! `ret`, `call *`, `jmp *` not safe beyond this point. */
> - /* SPEC_CTRL_EXIT_TO_SVM (nothing currently) */
> + /* SPEC_CTRL_EXIT_TO_SVM Req: Clob:
> C */
> + ALTERNATIVE "", STR(mov %rbx, %rdi; mov %rsp, %rsi),
> X86_FEATURE_SC_MSR_HVM
> + ALTERNATIVE "", STR(call vmentry_spec_ctrl), X86_FEATURE_SC_MSR_HVM
Both this and ...
> @@ -86,8 +86,10 @@ __UNLIKELY_END(nsvm_hap)
>
> GET_CURRENT(bx)
>
> - /* SPEC_CTRL_ENTRY_FROM_SVM Req: b=curr %rsp=regs/cpuinfo, Clob:
> ac */
> + /* SPEC_CTRL_ENTRY_FROM_SVM Req: Clob:
> C */
> ALTERNATIVE "", DO_OVERWRITE_RSB, X86_FEATURE_SC_RSB_HVM
> + ALTERNATIVE "", STR(mov %rsp, %rdi), X86_FEATURE_SC_MSR_HVM
> + ALTERNATIVE "", STR(call vmexit_spec_ctrl), X86_FEATURE_SC_MSR_HVM
> /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */
... this now effectively violate what the warning comment says, as there
is a RET involved in the C call. If this is not a problem for some reason,
I'd like to ask that the comments be updated accordingly.
Jan
|
