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Date: Wed, 5 Apr 2023 03:10:33 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "Christopherson,, Sean" <seanjc@...gle.com>
CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"pbonzini@...hat.com" <pbonzini@...hat.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: VMX: Get rid of hard-coded value around
IA32_VMX_BASIC
On Tue, 2023-04-04 at 17:18 -0700, Sean Christopherson wrote:
> On Thu, Mar 30, 2023, Kai Huang wrote:
> > Currently, setup_vmcs_config() uses hard-coded values when performing
> > sanity check on the value of IA32_VMX_BASIC MSR and setting up the three
> > members of 'vmcs_config': size, revison_id and basic_cap. However, the
> > kernel actually already has macro definitions for those relevant bits in
> > asm/msr-index.h and functions to get revision_id and size in asm/vmx.h.
> >
> > Add the missing helper function to get the basic_cap, and use those
> > macros and helper functions in setup_vmcs_config() to get rid of those
> > hard-coded values.
> >
> > No functional change intended.
> >
> > Signed-off-by: Kai Huang <kai.huang@...el.com>
> > ---
> > arch/x86/include/asm/vmx.h | 5 +++++
> > arch/x86/kvm/vmx/vmx.c | 17 +++++++++--------
> > 2 files changed, 14 insertions(+), 8 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
> > index 498dc600bd5c..2b488895fe0e 100644
> > --- a/arch/x86/include/asm/vmx.h
> > +++ b/arch/x86/include/asm/vmx.h
> > @@ -141,6 +141,11 @@ static inline u32 vmx_basic_vmcs_size(u64 vmx_basic)
> > return (vmx_basic & GENMASK_ULL(44, 32)) >> 32;
> > }
> >
> > +static inline u32 vmx_basic_cap(u64 vmx_basic)
>
> I would omit this helper and just open code the ugliness, purely because what
> it's tracking is completely random.
>
> > +{
> > + return (vmx_basic & ~GENMASK_ULL(44, 32)) >> 32;
> > +}
> > +
>
> ...
>
> > #ifdef CONFIG_X86_64
> > /* IA-32 SDM Vol 3B: 64-bit CPUs always have VMX_BASIC_MSR[48]==0. */
> > - if (vmx_msr_high & (1u<<16))
> > + if (basic_msr & VMX_BASIC_64)
> > return -EIO;
> > #endif
> >
> > /* Require Write-Back (WB) memory type for VMCS accesses. */
> > - if (((vmx_msr_high >> 18) & 15) != 6)
> > + if (((basic_msr & VMX_BASIC_MEM_TYPE_MASK) >> VMX_BASIC_MEM_TYPE_SHIFT)
> > + != VMX_BASIC_MEM_TYPE_WB)
>
> This one is worthy of a helper, e.g.
>
> if (vmx_basic_vmcs_memtype(basic_msr) != VMX_BASIC_MEM_TYPE_WB)
> return -EIO;
>
>
> > return -EIO;
> >
> > rdmsrl(MSR_IA32_VMX_MISC, misc_msr);
> >
> > - vmcs_conf->size = vmx_msr_high & 0x1fff;
> > - vmcs_conf->basic_cap = vmx_msr_high & ~0x1fff;
> > + vmcs_conf->size = vmx_basic_vmcs_size(basic_msr);
> > + vmcs_conf->basic_cap = vmx_basic_cap(basic_msr);
>
> Actually, looking at this more closely, splitting up the basic MSR during setup
> is silly. None of the usage is in hot paths, and cpu_has_vmx_basic_inout() is
> downright bizarre with the current code.
>
> Rather than do all of these weird dances, what about saving the full/raw MSR in
> the config, and then using the helpers to extract info as needed? E.g. the below
> over a few patches. As a bonus (maybe), KVM will sanity check the entire MSR
> across CPUs.
Fine to me. I'll rewrite this in one or more patches as you suggested and post
again. Thanks!
>
> ---
> arch/x86/include/asm/vmx.h | 5 +++++
> arch/x86/kvm/vmx/capabilities.h | 6 ++----
> arch/x86/kvm/vmx/vmx.c | 22 +++++++++-------------
> 3 files changed, 16 insertions(+), 17 deletions(-)
>
> diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
> index 498dc600bd5c..b21dcd128add 100644
> --- a/arch/x86/include/asm/vmx.h
> +++ b/arch/x86/include/asm/vmx.h
> @@ -141,6 +141,11 @@ static inline u32 vmx_basic_vmcs_size(u64 vmx_basic)
> return (vmx_basic & GENMASK_ULL(44, 32)) >> 32;
> }
>
> +static inline u32 vmx_basic_vmcs_memtype(u64 vmx_basic)
> +{
> + return (vmx_basic & VMX_BASIC_MEM_TYPE_MASK) >> VMX_BASIC_MEM_TYPE_SHIFT;
> +}
> +
> static inline int vmx_misc_preemption_timer_rate(u64 vmx_misc)
> {
> return vmx_misc & VMX_MISC_PREEMPTION_TIMER_RATE_MASK;
> diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
> index 45162c1bcd8f..d8849e42ca80 100644
> --- a/arch/x86/kvm/vmx/capabilities.h
> +++ b/arch/x86/kvm/vmx/capabilities.h
> @@ -54,9 +54,7 @@ struct nested_vmx_msrs {
> };
>
> struct vmcs_config {
> - int size;
> - u32 basic_cap;
> - u32 revision_id;
> + u64 basic;
> u32 pin_based_exec_ctrl;
> u32 cpu_based_exec_ctrl;
> u32 cpu_based_2nd_exec_ctrl;
> @@ -76,7 +74,7 @@ extern struct vmx_capability vmx_capability __ro_after_init;
>
> static inline bool cpu_has_vmx_basic_inout(void)
> {
> - return (((u64)vmcs_config.basic_cap << 32) & VMX_BASIC_INOUT);
> + return vmcs_config.basic & VMX_BASIC_INOUT;
> }
>
> static inline bool cpu_has_virtual_nmis(void)
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index d7bf14abdba1..64a43c2d72e9 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -2597,13 +2597,13 @@ static u64 adjust_vmx_controls64(u64 ctl_opt, u32 msr)
> static int setup_vmcs_config(struct vmcs_config *vmcs_conf,
> struct vmx_capability *vmx_cap)
> {
> - u32 vmx_msr_low, vmx_msr_high;
> u32 _pin_based_exec_control = 0;
> u32 _cpu_based_exec_control = 0;
> u32 _cpu_based_2nd_exec_control = 0;
> u64 _cpu_based_3rd_exec_control = 0;
> u32 _vmexit_control = 0;
> u32 _vmentry_control = 0;
> + u64 basic_msr;
> u64 misc_msr;
> int i;
>
> @@ -2722,29 +2722,25 @@ static int setup_vmcs_config(struct vmcs_config *vmcs_conf,
> _vmexit_control &= ~x_ctrl;
> }
>
> - rdmsr(MSR_IA32_VMX_BASIC, vmx_msr_low, vmx_msr_high);
> + rdmsrl(MSR_IA32_VMX_BASIC, basic_msr);
>
> /* IA-32 SDM Vol 3B: VMCS size is never greater than 4kB. */
> - if ((vmx_msr_high & 0x1fff) > PAGE_SIZE)
> + if (vmx_basic_vmcs_size(basic_msr) > PAGE_SIZE)
> return -EIO;
>
> #ifdef CONFIG_X86_64
> /* IA-32 SDM Vol 3B: 64-bit CPUs always have VMX_BASIC_MSR[48]==0. */
> - if (vmx_msr_high & (1u<<16))
> + if (basic_msr & VMX_BASIC_64)
> return -EIO;
> #endif
>
> /* Require Write-Back (WB) memory type for VMCS accesses. */
> - if (((vmx_msr_high >> 18) & 15) != 6)
> + if (vmx_basic_vmcs_memtype(basic_msr) != VMX_BASIC_MEM_TYPE_WB)
> return -EIO;
>
> rdmsrl(MSR_IA32_VMX_MISC, misc_msr);
>
> - vmcs_conf->size = vmx_msr_high & 0x1fff;
> - vmcs_conf->basic_cap = vmx_msr_high & ~0x1fff;
> -
> - vmcs_conf->revision_id = vmx_msr_low;
> -
> + vmcs_conf->basic = basic_msr;
> vmcs_conf->pin_based_exec_ctrl = _pin_based_exec_control;
> vmcs_conf->cpu_based_exec_ctrl = _cpu_based_exec_control;
> vmcs_conf->cpu_based_2nd_exec_ctrl = _cpu_based_2nd_exec_control;
> @@ -2883,13 +2879,13 @@ struct vmcs *alloc_vmcs_cpu(bool shadow, int cpu, gfp_t flags)
> if (!pages)
> return NULL;
> vmcs = page_address(pages);
> - memset(vmcs, 0, vmcs_config.size);
> + memset(vmcs, 0, vmx_basic_vmcs_size(vmcs_config.basic));
>
> /* KVM supports Enlightened VMCS v1 only */
> if (kvm_is_using_evmcs())
> vmcs->hdr.revision_id = KVM_EVMCS_VERSION;
> else
> - vmcs->hdr.revision_id = vmcs_config.revision_id;
> + vmcs->hdr.revision_id = vmx_basic_vmcs_revision_id(vmcs_config.basic);
>
> if (shadow)
> vmcs->hdr.shadow_vmcs = 1;
> @@ -2982,7 +2978,7 @@ static __init int alloc_kvm_area(void)
> * physical CPU.
> */
> if (kvm_is_using_evmcs())
> - vmcs->hdr.revision_id = vmcs_config.revision_id;
> + vmcs->hdr.revision_id = vmx_basic_vmcs_revision_id(vmcs_config.basic);
>
> per_cpu(vmxarea, cpu) = vmcs;
> }
>
> base-commit: f6cde92083dec5cf424504d7029acdffbe5beed8
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