linux-kernel - Re: [RFC PATCH 6/6] KVM: SVM: Pin SEV pages in MMU during sev_launch_update

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Date:   Wed, 19 Jan 2022 17:05:52 +0530
From:   "Nikunj A. Dadhania" <nikunj@....com>
To:     "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Peter Gonda <pgonda@...gle.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Bharata B Rao <bharata@....com>
Subject: Re: [RFC PATCH 6/6] KVM: SVM: Pin SEV pages in MMU during
 sev_launch_update_data()

On 1/18/2022 10:59 PM, Maciej S. Szmigiero wrote:
> On 18.01.2022 16:00, Maciej S. Szmigiero wrote:
>> Hi Nikunj,
>>
>> On 18.01.2022 12:06, Nikunj A Dadhania wrote:
>>> From: Sean Christopherson <sean.j.christopherson@...el.com>
>>>
>>> Pin the memory for the data being passed to launch_update_data()
>>> because it gets encrypted before the guest is first run and must
>>> not be moved which would corrupt it.
>>>
>>> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
>>> [ * Changed hva_to_gva() to take an extra argument and return gpa_t.
>>>    * Updated sev_pin_memory_in_mmu() error handling.
>>>    * As pinning/unpining pages is handled within MMU, removed
>>>      {get,put}_user(). ]
>>> Signed-off-by: Nikunj A Dadhania <nikunj@....com>
>>> ---
>>>   arch/x86/kvm/svm/sev.c | 122 ++++++++++++++++++++++++++++++++++++++++-
>>>   1 file changed, 119 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
>>> index 14aeccfc500b..1ae714e83a3c 100644
>>> --- a/arch/x86/kvm/svm/sev.c
>>> +++ b/arch/x86/kvm/svm/sev.c
>>> @@ -22,6 +22,7 @@
>>>   #include <asm/trapnr.h>
>>>   #include <asm/fpu/xcr.h>
>>> +#include "mmu.h"
>>>   #include "x86.h"
>>>   #include "svm.h"
>>>   #include "svm_ops.h"
>>> @@ -490,6 +491,110 @@ static unsigned long get_num_contig_pages(unsigned long idx,
>>>       return pages;
>>>   }
>>> +#define SEV_PFERR_RO (PFERR_USER_MASK)
>>> +#define SEV_PFERR_RW (PFERR_WRITE_MASK | PFERR_USER_MASK)
>>> +
>>> +static struct kvm_memory_slot *hva_to_memslot(struct kvm *kvm,
>>> +                          unsigned long hva)
>>> +{
>>> +    struct kvm_memslots *slots = kvm_memslots(kvm);
>>> +    struct kvm_memory_slot *memslot;
>>> +    int bkt;
>>> +
>>> +    kvm_for_each_memslot(memslot, bkt, slots) {
>>> +        if (hva >= memslot->userspace_addr &&
>>> +            hva < memslot->userspace_addr +
>>> +            (memslot->npages << PAGE_SHIFT))
>>> +            return memslot;
>>> +    }
>>> +
>>> +    return NULL;
>>> +}
>>
>> We have kvm_for_each_memslot_in_hva_range() now, please don't do a linear
>> search through memslots.
>> You might need to move the aforementioned macro from kvm_main.c to some
>> header file, though.
> 
> Besides performance considerations I can't see the code here taking into
> account the fact that a hva can map to multiple memslots (they an overlap
> in the host address space).

You are right I was returning at the first match, looks like if I switch to using 
kvm_for_each_memslot_in_hva_range() it should take care of overlapping hva, 
is this understanding correct ?

Regards
Nikunj