Re: [PATCH v3 1/1] crypto: ccp - Make usage of sev_cmd_mutex more granular

[Sean Christopherson <seanjc@google.com>]

On Wed, Oct 21, 2026, Michael Roth wrote:
> The current code makes very coarse usage of the sev_cmd_mutex; for SEV
> firmware ioctls, it is essentially taken upon entry, and ends up
> wrapping a lot of potentially time-consuming prep work that may need to
> be done before issuing the actual firmware call, which is the main thing
> the mutex is meant to protect.
> 
> Additionally, some of that prep work involves
> copy_from_user()/copy_to_user() calls which can generate page faults and
> unecessarily lead to potential deadlock scenarios. No known case exists
> in current upstream, but with the upcoming KVM/guest_memfd support for
> in-place conversion of the same PFN between shared/private state, a
> special fault handler is needed that could theoretically deadlock if a
> malicious user tries to use guest_memfd pages as the source/target of
> previously mentioned copy_from_user()/copy_to_user() scenarios.
> 
> There's no reason to hold the mutex across these problematic scenarios
> however. Push sev_cmd_mutex down from the top-level sev_ioctl() into
> each individual command handler, acquiring the mutex mainly around the
> platform state transitions and firmware command execution.
> 
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Co-developed-by: Ackerley Tng <ackerleytng@google.com>
> Signed-off-by: Ackerley Tng <ackerleytng@google.com>
> Signed-off-by: Michael Roth <michael.roth@amd.com>
> ---

Tested-by: Sean Christopherson <seanjc@google.com>