linux-kernel - Re: [PATCH 1/2] KVM: x86: Add emulation support for #GP triggered by VM instructions

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Message-Id: <130DAF1C-06FC-4335-97AD-691B39A2C847@amacapital.net>
Date:   Tue, 12 Jan 2021 07:11:58 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Wei Huang <wei.huang2@....com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, pbonzini@...hat.com,
        seanjc@...gle.com, joro@...tes.org, bp@...en8.de,
        tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
        jmattson@...gle.com, wanpengli@...cent.com, bsd@...hat.com,
        dgilbert@...hat.com, wei.huang2@....com, mlevitsk@...hat.com
Subject: Re: [PATCH 1/2] KVM: x86: Add emulation support for #GP triggered by VM instructions


> On Jan 12, 2021, at 4:15 AM, Vitaly Kuznetsov <vkuznets@...hat.com> wrote:
> 
> Wei Huang <wei.huang2@....com> writes:
> 
>> From: Bandan Das <bsd@...hat.com>
>> 
>> While running VM related instructions (VMRUN/VMSAVE/VMLOAD), some AMD
>> CPUs check EAX against reserved memory regions (e.g. SMM memory on host)
>> before checking VMCB's instruction intercept. If EAX falls into such
>> memory areas, #GP is triggered before VMEXIT. This causes problem under
>> nested virtualization. To solve this problem, KVM needs to trap #GP and
>> check the instructions triggering #GP. For VM execution instructions,
>> KVM emulates these instructions; otherwise it re-injects #GP back to
>> guest VMs.
>> 
>> Signed-off-by: Bandan Das <bsd@...hat.com>
>> Co-developed-by: Wei Huang <wei.huang2@....com>
>> Signed-off-by: Wei Huang <wei.huang2@....com>
>> ---
>> arch/x86/include/asm/kvm_host.h |   8 +-
>> arch/x86/kvm/mmu.h              |   1 +
>> arch/x86/kvm/mmu/mmu.c          |   7 ++
>> arch/x86/kvm/svm/svm.c          | 157 +++++++++++++++++++-------------
>> arch/x86/kvm/svm/svm.h          |   8 ++
>> arch/x86/kvm/vmx/vmx.c          |   2 +-
>> arch/x86/kvm/x86.c              |  37 +++++++-
>> 7 files changed, 146 insertions(+), 74 deletions(-)
>> 
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index 3d6616f6f6ef..0ddc309f5a14 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -1450,10 +1450,12 @@ extern u64 kvm_mce_cap_supported;
>>  *                 due to an intercepted #UD (see EMULTYPE_TRAP_UD).
>>  *                 Used to test the full emulator from userspace.
>>  *
>> - * EMULTYPE_VMWARE_GP - Set when emulating an intercepted #GP for VMware
>> + * EMULTYPE_PARAVIRT_GP - Set when emulating an intercepted #GP for VMware
>>  *            backdoor emulation, which is opt in via module param.
>>  *            VMware backoor emulation handles select instructions
>> - *            and reinjects the #GP for all other cases.
>> + *            and reinjects #GP for all other cases. This also
>> + *            handles other cases where #GP condition needs to be
>> + *            handled and emulated appropriately
>>  *
>>  * EMULTYPE_PF - Set when emulating MMIO by way of an intercepted #PF, in which
>>  *         case the CR2/GPA value pass on the stack is valid.
>> @@ -1463,7 +1465,7 @@ extern u64 kvm_mce_cap_supported;
>> #define EMULTYPE_SKIP            (1 << 2)
>> #define EMULTYPE_ALLOW_RETRY_PF        (1 << 3)
>> #define EMULTYPE_TRAP_UD_FORCED        (1 << 4)
>> -#define EMULTYPE_VMWARE_GP        (1 << 5)
>> +#define EMULTYPE_PARAVIRT_GP        (1 << 5)
>> #define EMULTYPE_PF            (1 << 6)
>> 
>> int kvm_emulate_instruction(struct kvm_vcpu *vcpu, int emulation_type);
>> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
>> index 581925e476d6..1a2fff4e7140 100644
>> --- a/arch/x86/kvm/mmu.h
>> +++ b/arch/x86/kvm/mmu.h
>> @@ -219,5 +219,6 @@ int kvm_arch_write_log_dirty(struct kvm_vcpu *vcpu);
>> 
>> int kvm_mmu_post_init_vm(struct kvm *kvm);
>> void kvm_mmu_pre_destroy_vm(struct kvm *kvm);
>> +bool kvm_is_host_reserved_region(u64 gpa);
> 
> Just a suggestion: "kvm_gpa_in_host_reserved()" maybe? 
> 
>> 
>> #endif
>> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
>> index 6d16481aa29d..c5c4aaf01a1a 100644
>> --- a/arch/x86/kvm/mmu/mmu.c
>> +++ b/arch/x86/kvm/mmu/mmu.c
>> @@ -50,6 +50,7 @@
>> #include <asm/io.h>
>> #include <asm/vmx.h>
>> #include <asm/kvm_page_track.h>
>> +#include <asm/e820/api.h>
>> #include "trace.h"
>> 
>> extern bool itlb_multihit_kvm_mitigation;
>> @@ -5675,6 +5676,12 @@ void kvm_mmu_slot_set_dirty(struct kvm *kvm,
>> }
>> EXPORT_SYMBOL_GPL(kvm_mmu_slot_set_dirty);
>> 
>> +bool kvm_is_host_reserved_region(u64 gpa)
>> +{
>> +    return e820__mbapped_raw_any(gpa-1, gpa+1, E820_TYPE_RESERVED);
>> +}
> 
> While _e820__mapped_any()'s doc says '..  checks if any part of the
> range <start,end> is mapped ..' it seems to me that the real check is
> [start, end) so we should use 'gpa' instead of 'gpa-1', no?

Why do you need to check GPA at all?