Re: [PATCH v12 22/29] KVM: SEV: Implement gmem hook for invalidating private pages

[Paolo Bonzini <pbonzini@redhat.com>]

On 3/29/24 23:58, Michael Roth wrote:
> +		/*
> +		 * If an unaligned PFN corresponds to a 2M region assigned as a
> +		 * large page in he RMP table, PSMASH the region into individual
> +		 * 4K RMP entries before attempting to convert a 4K sub-page.
> +		 */
> +		if (!use_2m_update && rmp_level > PG_LEVEL_4K) {
> +			rc = snp_rmptable_psmash(pfn);
> +			if (rc)
> +				pr_err_ratelimited("SEV: Failed to PSMASH RMP entry for PFN 0x%llx error %d\n",
> +						   pfn, rc);
> +		}

Ignoring the PSMASH failure is pretty scary...  At this point 
.free_folio cannot fail, should the psmash part of this patch be done in 
kvm_gmem_invalidate_begin() before kvm_mmu_unmap_gfn_range()?

Also, can you get PSMASH_FAIL_INUSE and if so what's the best way to 
address it?  Should fallocate() return -EBUSY?

Thanks,

Paolo


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Subject: Re: [PATCH v12 22/29] KVM: SEV: Implement gmem hook for invalidating
 private pages
To: Michael Roth <michael.roth@amd.com>, kvm@vger.kernel.org
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References: <20240329225835.400662-1-michael.roth@amd.com>
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On 3/29/24 23:58, Michael Roth wrote:
> +		/*
> +		 * If an unaligned PFN corresponds to a 2M region assigned as a
> +		 * large page in he RMP table, PSMASH the region into individual
> +		 * 4K RMP entries before attempting to convert a 4K sub-page.
> +		 */
> +		if (!use_2m_update && rmp_level > PG_LEVEL_4K) {
> +			rc = snp_rmptable_psmash(pfn);
> +			if (rc)
> +				pr_err_ratelimited("SEV: Failed to PSMASH RMP entry for PFN 0x%llx error %d\n",
> +						   pfn, rc);
> +		}

Ignoring the PSMASH failure is pretty scary...  At this point 
.free_folio cannot fail, should the psmash part of this patch be done in 
kvm_gmem_invalidate_begin() before kvm_mmu_unmap_gfn_range()?

Also, can you get PSMASH_FAIL_INUSE and if so what's the best way to 
address it?  Should fallocate() return -EBUSY?

Thanks,

Paolo


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On 3/29/24 23:58, Michael Roth wrote:
> +		/*
> +		 * If an unaligned PFN corresponds to a 2M region assigned as a
> +		 * large page in he RMP table, PSMASH the region into individual
> +		 * 4K RMP entries before attempting to convert a 4K sub-page.
> +		 */
> +		if (!use_2m_update && rmp_level > PG_LEVEL_4K) {
> +			rc = snp_rmptable_psmash(pfn);
> +			if (rc)
> +				pr_err_ratelimited("SEV: Failed to PSMASH RMP entry for PFN 0x%llx error %d\n",
> +						   pfn, rc);
> +		}

Ignoring the PSMASH failure is pretty scary...  At this point 
free_folio cannot fail, should the psmash part of this patch be done in 
kvm_gmem_invalidate_begin() before kvm_mmu_unmap_gfn_range()?

Also, can you get PSMASH_FAIL_INUSE and if so what's the best way to 
address it?  Should fallocate() return -EBUSY?

Thanks,

Paolo