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From:   "Kalra, Ashish" <Ashish.Kalra@amd.com>
To:     Jarkko Sakkinen <jarkko@kernel.org>
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Subject: RE: [PATCH Part2 v6 09/49] x86/fault: Add support to handle the RMP
 fault for user address
Thread-Topic: [PATCH Part2 v6 09/49] x86/fault: Add support to handle the RMP
 fault for user address
Thread-Index: AQHYleaS30zm/ve2UUW13wSedLDd3a16xpjA
Date:   Tue, 12 Jul 2022 14:29:18 +0000
Message-ID: <SN6PR12MB27676FD80E6B20D6B8459EC28E869@SN6PR12MB2767.namprd12.prod.outlook.com>
References: <cover.1655761627.git.ashish.kalra@amd.com>
 <0ecb0a4781be933fcadeb56a85070818ef3566e7.1655761627.git.ashish.kalra@amd.com>
 <Ys1hrq+vFbxRJbra@kernel.org>
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[AMD Official Use Only - General]

>> +static int handle_user_rmp_page_fault(struct pt_regs *regs, unsigned lo=
ng error_code,
>> +				      unsigned long address)
>> +{
>> +	int rmp_level, level;
>> +	pte_t *pte;
>> +	u64 pfn;
>> +
>> +	pte =3D lookup_address_in_mm(current->mm, address, &level);

>As discussed in [1], the lookup should be done in kvm->mm, along the lines=
 of host_pfn_mapping_level().

With lookup_address_in_mm() now removed in 5.19, this is now using lookup_a=
ddress_in_pgd() though still using non init-mm, and as mentioned here in [1=
], it makes sense to
not use lookup_address_in_pgd() as it does not play nice with userspace map=
pings, e.g. doesn't disable IRQs to block TLB shootdowns and doesn't use RE=
AD_ONCE()
to ensure an upper level entry isn't converted to a huge page between check=
ing the PAGE_SIZE bit and grabbing the address of the next level down.

But is KVM going to provide its own variant of lookup_address_in_pgd() that=
 is safe for use with user addresses, i.e., a generic version of lookup_add=
ress() on kvm->mm or we need to
duplicate page table walking code of host_pfn_mapping_level() ?

Thanks,
Ashish

>[1] https://nam11.safelinks.protection.outlook.com/?url=3Dhttps%3A%2F%2Flo=
re.kernel.org%2Fkvm%2FYmwIi3bXr%252F1yhYV%252F%40google.com%2F&amp;data=3D0=
5%7C01%7CAshish.Kalra%40amd.com%>7Ce300014162fc4d8b452708da63fdb970%7C3dd89=
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3000%>7C%7C%7C&amp;sdata=3DGxPrEUxuVNEm6COdfHCILOwp9yuX48gpoYmtrOwMx8Q%3D&a=
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