RE: [PATCH 2/5] KVM: x86/mmu: Fine-grained check of whether a invalid & RAM PFN is MMIO

Tian, Kevin
2024-05-07T08:39:31Z

> From: Zhao, Yan Y <yan.y.zhao@intel.com>
> Sent: Tuesday, May 7, 2024 2:20 PM
> @@ -101,9 +101,21 @@ static bool kvm_is_mmio_pfn(kvm_pfn_t pfn)
> */
> (!pat_enabled() ||
> pat_pfn_immune_to_uc_mtrr(pfn));
>
> + /*
> + * If the PFN is invalid and not RAM in raw e820 table, keep treating it
> + * as MMIO.
> + *
> + * If the PFN is invalid and is RAM in raw e820 table,
> + * - if PAT is not enabled, always treat the PFN as MMIO to avoid
> futher
> + * checking of MTRRs.
> + * - if PAT is enabled, treat the PFN as MMIO if its PAT is UC/WC/UC-
> in
> + * primary MMU.
> + * to prevent guest cacheable access to MMIO PFNs.
> + */
> return !e820__mapped_raw_any(pfn_to_hpa(pfn),
> pfn_to_hpa(pfn + 1) - 1,
> - E820_TYPE_RAM);
> + E820_TYPE_RAM) ? true :
> + (!pat_enabled() ||
> pat_pfn_immune_to_uc_mtrr(pfn));

Is it for another theoretical problem in case the primary
mmu uses a non-WB type on a invalid RAM-type pfn so
you want to do additional scrutiny here?