linux-kernel - Re: [PATCH RFC v7 01/64] KVM: Fix memslot boundary condition for large page

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Message-ID: <2ebc9510-d7bf-a46d-6e78-f9e528b79501@amd.com>
Date:   Thu, 5 Jan 2023 09:38:59 +0530
From:   "Nikunj A. Dadhania" <nikunj@....com>
To:     Chao Peng <chao.p.peng@...ux.intel.com>,
        Jarkko Sakkinen <jarkko@...nel.org>
Cc:     Michael Roth <michael.roth@....com>, kvm@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
        ardb@...nel.org, pbonzini@...hat.com, seanjc@...gle.com,
        vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com,
        luto@...nel.org, dave.hansen@...ux.intel.com, slp@...hat.com,
        pgonda@...gle.com, peterz@...radead.org,
        srinivas.pandruvada@...ux.intel.com, rientjes@...gle.com,
        dovmurik@...ux.ibm.com, tobin@....com, bp@...en8.de,
        vbabka@...e.cz, kirill@...temov.name, ak@...ux.intel.com,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com,
        dgilbert@...hat.com, ashish.kalra@....com, harald@...fian.com
Subject: Re: [PATCH RFC v7 01/64] KVM: Fix memslot boundary condition for
 large page



On 05/01/23 09:04, Chao Peng wrote:
> On Wed, Jan 04, 2023 at 12:01:05PM +0000, Jarkko Sakkinen wrote:
>> On Wed, Dec 14, 2022 at 01:39:53PM -0600, Michael Roth wrote:
>>> From: Nikunj A Dadhania <nikunj@....com>
>>>
>>> Aligned end boundary causes a kvm crash, handle the case.
>>>
>>
>> Link: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fkvm%2F20221202061347.1070246-8-chao.p.peng%40linux.intel.com%2F&data=05%7C01%7Cnikunj.dadhania%40amd.com%7C7a95933fac1b433e339c08daeece6c2c%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638084867591405299%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=vDEu9Uxs0QRdzbUkJbE2LsJnMHJJHBdQijkePbE2woc%3D&reserved=0
>>
>> Chao, are you aware of this issue already?
> 
> Thanks Jarkko adding me. I'm not aware of there is a fix.

It was discussed here: https://lore.kernel.org/all/e234d307-0b05-6548-5882-c24fc32c8e77@amd.com/

I was hitting this with one of the selftests case.

> 
>>
>>> Signed-off-by: Nikunj A Dadhania <nikunj@....com>
>>> Signed-off-by: Michael Roth <michael.roth@....com>
>>> ---
>>>  arch/x86/kvm/mmu/mmu.c | 3 +++
>>>  1 file changed, 3 insertions(+)
>>>
>>> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
>>> index b1953ebc012e..b3ffc61c668c 100644
>>> --- a/arch/x86/kvm/mmu/mmu.c
>>> +++ b/arch/x86/kvm/mmu/mmu.c
>>> @@ -7159,6 +7159,9 @@ static void kvm_update_lpage_private_shared_mixed(struct kvm *kvm,
>>>  		for (gfn = first + pages; gfn < last; gfn += pages)
>>>  			linfo_set_mixed(gfn, slot, level, false);
>>>  
>>> +		if (gfn == last)
>>> +			goto out;
>>> +
> 
> Nikunj or Michael, could you help me understand in which case it causes
> a KVM crash? To me, even the end is aligned to huge page boundary, but:
>     last = (end - 1) & mask;
> so 'last' is the base address for the last effective huage page. Even
> when gfn == last, it should still a valid page and needs to be updated
> for mem_attrs, correct?

Yes, that is correct with: last = (end - 1) & mask;

We can drop this patch from SNP series.

Regards
Nikunj