On 31/01/19 17:09, Yu Zhang wrote:
> Previously, 'commit 372fddf70904 ("x86/mm: Introduce the 'no5lvl' kernel
> parameter")' cleared X86_FEATURE_LA57 in boot_cpu_data, if Linux chooses
> to not run in 5-level paging mode. Yet boot_cpu_data is queried by
> do_cpuid_ent() as the host capability later when creating vcpus, and Qemu
> will not be able to detect this feature and create VMs with LA57 feature.
>
> As discussed earlier, VMs can still benefit from extended linear address
> width, e.g. to enhance features like ASLR. So we would like to fix this,
> by return the true hardware capability when Qemu queries.
>
> Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
> ---
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: "Radim Krčmář" <rkrcmar@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
> arch/x86/kvm/cpuid.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index bbffa6c..c07958b 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -335,6 +335,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
> unsigned f_xsaves = kvm_x86_ops->xsaves_supported() ? F(XSAVES) : 0;
> unsigned f_umip = kvm_x86_ops->umip_emulated() ? F(UMIP) : 0;
> unsigned f_intel_pt = kvm_x86_ops->pt_supported() ? F(INTEL_PT) : 0;
> + unsigned f_la57 = 0;
>
> /* cpuid 1.edx */
> const u32 kvm_cpuid_1_edx_x86_features =
> @@ -489,7 +490,10 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
> // TSC_ADJUST is emulated
> entry->ebx |= F(TSC_ADJUST);
> entry->ecx &= kvm_cpuid_7_0_ecx_x86_features;
> + f_la57 = entry->ecx & F(LA57);
> cpuid_mask(&entry->ecx, CPUID_7_ECX);
> + /* Set LA57 based on hardware capability. */
> + entry->ecx |= f_la57;
> entry->ecx |= f_umip;
> /* PKU is not yet implemented for shadow paging. */
> if (!tdp_enabled || !boot_cpu_has(X86_FEATURE_OSPKE))
>
Queued for 5.1 past merge window, thanks.
Paolo
