Re: [PATCH] KVM: x86: Add SRCU protection for KVM_GET_SREGS2

[Vasiliy Kovalev <kovalev@altlinux.org>]

On 1/23/26 20:24, Sean Christopherson wrote:
> On Fri, Jan 16, 2026, Vasiliy Kovalev wrote:
>> ---
>> Note 1: commit 85e5ba83c016 ("KVM: x86: Do all post-set CPUID processing
>> during vCPU creation") in v6.14+ reduces the likelihood of hitting this
>> path by ensuring proper MMU initialization, but does not eliminate the
>> requirement for SRCU protection when accessing guest memory.
>>
>> Note 2: KVM_SET_SREGS2 is not modified because __set_sregs_common()
>> already acquires SRCU when update_pdptrs=true, which covers the case
>> when PDPTRs must be loaded from guest memory.
> 
> On the topic of the update_pdptrs behavior, what if we scope the fix to precisely
> reading the PDPTRs?  Not for performance reasons, but for documentation purposes,
> e.g. so that future readers don't look at __get_sregs() and wonder why that call
> isn't wrapped with SRCU protection.

Agreed, moving the lock inside __get_sregs2() makes the requirements
clearer. I've verified it fixes the issue and sent v2:
https://lore.kernel.org/all/20260123222801.646123-1-kovalev@altlinux.org/

-- 
Thanks,
Vasiliy