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Message-ID: <dfa5fd77-09e2-4133-a757-8c407593c6c9@intel.com>
Date: Tue, 26 Nov 2024 18:15:28 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: Nikolay Borisov <nik.borisov@...e.com>, pbonzini@...hat.com,
seanjc@...gle.com, kvm@...r.kernel.org, dave.hansen@...ux.intel.com
Cc: rick.p.edgecombe@...el.com, kai.huang@...el.com,
reinette.chatre@...el.com, xiaoyao.li@...el.com,
tony.lindgren@...ux.intel.com, binbin.wu@...ux.intel.com,
dmatlack@...gle.com, isaku.yamahata@...el.com, linux-kernel@...r.kernel.org,
x86@...nel.org, yan.y.zhao@...el.com, chao.gao@...el.com,
weijiang.yang@...el.com
Subject: Re: [PATCH 3/7] KVM: TDX: vcpu_run: save/restore host state(host
kernel gs)
On 25/11/24 16:12, Nikolay Borisov wrote:
>
>
> On 21.11.24 г. 22:14 ч., Adrian Hunter wrote:
>> From: Isaku Yamahata <isaku.yamahata@...el.com>
>>
>> On entering/exiting TDX vcpu, preserved or clobbered CPU state is different
>> from the VMX case. Add TDX hooks to save/restore host/guest CPU state.
>> Save/restore kernel GS base MSR.
>>
>> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
>> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
>> Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
>> ---
>> TD vcpu enter/exit v1:
>> - Clarify comment (Binbin)
>> - Use lower case preserved and add the for VMX in log (Tony)
>> - Fix bisectability issue with includes (Kai)
>> ---
>> arch/x86/kvm/vmx/main.c | 24 ++++++++++++++++++--
>> arch/x86/kvm/vmx/tdx.c | 46 ++++++++++++++++++++++++++++++++++++++
>> arch/x86/kvm/vmx/tdx.h | 4 ++++
>> arch/x86/kvm/vmx/x86_ops.h | 4 ++++
>> 4 files changed, 76 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
>> index 44ec6005a448..3a8ffc199be2 100644
>> --- a/arch/x86/kvm/vmx/main.c
>> +++ b/arch/x86/kvm/vmx/main.c
>> @@ -129,6 +129,26 @@ static void vt_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>> vmx_vcpu_load(vcpu, cpu);
>> }
>> +static void vt_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
>> +{
>> + if (is_td_vcpu(vcpu)) {
>> + tdx_prepare_switch_to_guest(vcpu);
>> + return;
>> + }
>> +
>> + vmx_prepare_switch_to_guest(vcpu);
>> +}
>> +
>> +static void vt_vcpu_put(struct kvm_vcpu *vcpu)
>> +{
>> + if (is_td_vcpu(vcpu)) {
>> + tdx_vcpu_put(vcpu);
>> + return;
>> + }
>> +
>> + vmx_vcpu_put(vcpu);
>> +}
>> +
>> static int vt_vcpu_pre_run(struct kvm_vcpu *vcpu)
>> {
>> if (is_td_vcpu(vcpu))
>> @@ -250,9 +270,9 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
>> .vcpu_free = vt_vcpu_free,
>> .vcpu_reset = vt_vcpu_reset,
>> - .prepare_switch_to_guest = vmx_prepare_switch_to_guest,
>> + .prepare_switch_to_guest = vt_prepare_switch_to_guest,
>> .vcpu_load = vt_vcpu_load,
>> - .vcpu_put = vmx_vcpu_put,
>> + .vcpu_put = vt_vcpu_put,
>> .update_exception_bitmap = vmx_update_exception_bitmap,
>> .get_feature_msr = vmx_get_feature_msr,
>> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
>> index 5fa5b65b9588..6e4ea2d420bc 100644
>> --- a/arch/x86/kvm/vmx/tdx.c
>> +++ b/arch/x86/kvm/vmx/tdx.c
>> @@ -1,6 +1,7 @@
>> // SPDX-License-Identifier: GPL-2.0
>> #include <linux/cleanup.h>
>> #include <linux/cpu.h>
>> +#include <linux/mmu_context.h>
>> #include <asm/tdx.h>
>> #include "capabilities.h"
>> #include "mmu.h"
>> @@ -9,6 +10,7 @@
>> #include "vmx.h"
>> #include "mmu/spte.h"
>> #include "common.h"
>> +#include "posted_intr.h"
>> #include <trace/events/kvm.h>
>> #include "trace.h"
>> @@ -605,6 +607,9 @@ int tdx_vcpu_create(struct kvm_vcpu *vcpu)
>> if ((kvm_tdx->xfam & XFEATURE_MASK_XTILE) == XFEATURE_MASK_XTILE)
>> vcpu->arch.xfd_no_write_intercept = true;
>> + tdx->host_state_need_save = true;
>> + tdx->host_state_need_restore = false;
>
> nit: Rather than have 2 separate values which actually work in tandem, why not define a u8 or even u32 and have a mask of the valid flags.
>
> So you can have something like:
>
> #define SAVE_HOST BIT(0)
> #define RESTORE_HOST BIT(1)
>
> tdx->state_flags = SAVE_HOST
>
> I don't know what are the plans for the future but there might be cases where you can have more complex flags composed of more simple ones.
>
There are really only 3 possibilities:
initial state (or after tdx_prepare_switch_to_host())
tdx->host_state_need_save = true;
tdx->host_state_need_restore = false;
After save (i.e. after tdx_prepare_switch_to_guest())
tdx->host_state_need_save = false
tdx->host_state_need_restore = false;
After enter/exit (i.e. after tdx_vcpu_enter_exit())
tdx->host_state_need_save = false
tdx->host_state_need_restore = true;
I can't think of good names, perhaps:
enum tdx_prepare_switch_state {
TDX_PREP_UNSAVED,
TDX_PREP_SAVED,
TDX_PREP_UNRESTORED,
};
>> tdx->state = VCPU_TD_STATE_UNINITIALIZED;
>> return 0;
>> @@ -631,6 +636,45 @@ void tdx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>> local_irq_enable();
>> }
>> +/*
>> + * Compared to vmx_prepare_switch_to_guest(), there is not much to do
>> + * as SEAMCALL/SEAMRET calls take care of most of save and restore.
>> + */
>> +void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
>> +{
>> + struct vcpu_tdx *tdx = to_tdx(vcpu);
>> +
>> + if (!tdx->host_state_need_save)
> if (!(tdx->state_flags & SAVE_HOST))
if (tdx->prep_switch_state != TDX_PREP_UNSAVED)
>> + return;
>> +
>> + if (likely(is_64bit_mm(current->mm)))
>> + tdx->msr_host_kernel_gs_base = current->thread.gsbase;
>> + else
>> + tdx->msr_host_kernel_gs_base = read_msr(MSR_KERNEL_GS_BASE);
>> +
>> + tdx->host_state_need_save = false;
>
> tdx->state &= ~SAVE_HOST
tdx->prep_switch_state = TDX_PREP_SAVED;
>> +}
>> +
>> +static void tdx_prepare_switch_to_host(struct kvm_vcpu *vcpu)
>> +{
>> + struct vcpu_tdx *tdx = to_tdx(vcpu);
>> +
>> + tdx->host_state_need_save = true;
>> + if (!tdx->host_state_need_restore)
> if (!(tdx->state_flags & RESTORE_HOST)
if (tdx->prep_switch_state != TDX_PREP_UNRESTORED)
>
>> + return;
>> +
>> + ++vcpu->stat.host_state_reload;
>> +
>> + wrmsrl(MSR_KERNEL_GS_BASE, tdx->msr_host_kernel_gs_base);
>> + tdx->host_state_need_restore = false;
tdx->prep_switch_state = TDX_PREP_UNSAVED;
>> +}
>> +
>> +void tdx_vcpu_put(struct kvm_vcpu *vcpu)
>> +{
>> + vmx_vcpu_pi_put(vcpu);
>> + tdx_prepare_switch_to_host(vcpu);
>> +}
>> +
>> void tdx_vcpu_free(struct kvm_vcpu *vcpu)
>> {
>> struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm);
>> @@ -732,6 +776,8 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
>> tdx_vcpu_enter_exit(vcpu);
>> + tdx->host_state_need_restore = true;
>
> tdx->state_flags |= RESTORE_HOST
tdx->prep_switch_state = TDX_PREP_UNRESTORED;
>
>> +
>> vcpu->arch.regs_avail &= ~VMX_REGS_LAZY_LOAD_SET;
>> trace_kvm_exit(vcpu, KVM_ISA_VMX);
>> diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h
>> index ebee1049b08b..48cf0a1abfcc 100644
>> --- a/arch/x86/kvm/vmx/tdx.h
>> +++ b/arch/x86/kvm/vmx/tdx.h
>> @@ -54,6 +54,10 @@ struct vcpu_tdx {
>> u64 vp_enter_ret;
>> enum vcpu_tdx_state state;
>> +
>> + bool host_state_need_save;
>> + bool host_state_need_restore;
>
> this would save having a discrete member for those boolean checks.
>
>> + u64 msr_host_kernel_gs_base;
>> };
>> void tdh_vp_rd_failed(struct vcpu_tdx *tdx, char *uclass, u32 field, u64 err);
>> diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
>> index 3d292a677b92..5bd45a720007 100644
>> --- a/arch/x86/kvm/vmx/x86_ops.h
>> +++ b/arch/x86/kvm/vmx/x86_ops.h
>> @@ -130,6 +130,8 @@ int tdx_vcpu_create(struct kvm_vcpu *vcpu);
>> void tdx_vcpu_free(struct kvm_vcpu *vcpu);
>> void tdx_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
>> fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit);
>> +void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu);
>> +void tdx_vcpu_put(struct kvm_vcpu *vcpu);
>> int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp);
>> @@ -161,6 +163,8 @@ static inline fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediat
>> {
>> return EXIT_FASTPATH_NONE;
>> }
>> +static inline void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu) {}
>> +static inline void tdx_vcpu_put(struct kvm_vcpu *vcpu) {}
>> static inline int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp) { return -EOPNOTSUPP; }
>>
>
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