linux-kernel - Re: [RFC PATCH 02/21] x86/virt/tdx: Enhance tdh_mem_page

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Message-ID: <a36db21a224a2314723f7681ad585cbbcfdc2e40.camel@intel.com>
Date: Tue, 13 May 2025 18:52:49 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "pbonzini@...hat.com" <pbonzini@...hat.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "Zhao, Yan Y" <yan.y.zhao@...el.com>
CC: "Shutemov, Kirill" <kirill.shutemov@...el.com>, "quic_eberman@...cinc.com"
	<quic_eberman@...cinc.com>, "Li, Xiaoyao" <xiaoyao.li@...el.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "Hansen, Dave"
	<dave.hansen@...el.com>, "david@...hat.com" <david@...hat.com>,
	"thomas.lendacky@....com" <thomas.lendacky@....com>, "tabba@...gle.com"
	<tabba@...gle.com>, "Li, Zhiquan1" <zhiquan1.li@...el.com>, "Du, Fan"
	<fan.du@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "michael.roth@....com"
	<michael.roth@....com>, "Weiny, Ira" <ira.weiny@...el.com>, "vbabka@...e.cz"
	<vbabka@...e.cz>, "binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>,
	"ackerleytng@...gle.com" <ackerleytng@...gle.com>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>, "Peng, Chao P" <chao.p.peng@...el.com>,
	"Annapurve, Vishal" <vannapurve@...gle.com>, "jroedel@...e.de"
	<jroedel@...e.de>, "Miao, Jun" <jun.miao@...el.com>, "pgonda@...gle.com"
	<pgonda@...gle.com>, "x86@...nel.org" <x86@...nel.org>
Subject: Re: [RFC PATCH 02/21] x86/virt/tdx: Enhance tdh_mem_page_aug() to
 support huge pages

On Thu, 2025-04-24 at 11:04 +0800, Yan Zhao wrote:
> Enhance the SEAMCALL wrapper tdh_mem_page_aug() to support huge pages.
> 
> Verify the validity of the level and ensure that the mapping range is fully
> contained within the page folio.
> 
> As a conservative solution, perform CLFLUSH on all pages to be mapped into
> the TD before invoking the SEAMCALL TDH_MEM_PAGE_AUG. This ensures that any
> dirty cache lines do not write back later and clobber TD memory.

This should have a brief background on why it doesn't use the arg - what is
deficient today. Also, an explanation of how it will be used (i.e. what types of
pages will be passed)

> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
> ---
>  arch/x86/virt/vmx/tdx/tdx.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index f5e2a937c1e7..a66d501b5677 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -1595,9 +1595,18 @@ u64 tdh_mem_page_aug(struct tdx_td *td, u64 gpa, int level, struct page *page, u
>  		.rdx = tdx_tdr_pa(td),
>  		.r8 = page_to_phys(page),
>  	};
> +	unsigned long nr_pages = 1 << (level * 9);
> +	struct folio *folio = page_folio(page);
> +	unsigned long idx = 0;
>  	u64 ret;
>  
> -	tdx_clflush_page(page);
> +	if (!(level >= TDX_PS_4K && level < TDX_PS_NR) ||
> +	    (folio_page_idx(folio, page) + nr_pages > folio_nr_pages(folio)))
> +		return -EINVAL;

Shouldn't KVM not try to map a huge page in this situation? Doesn't seem like a
job for the SEAMCALL wrapper.

> +
> +	while (nr_pages--)
> +		tdx_clflush_page(nth_page(page, idx++));

clflush_cache_range() is:
static void tdx_clflush_page(struct page *page)
{
	clflush_cache_range(page_to_virt(page), PAGE_SIZE);
}

So we have loops within loops...  Better to add an arg to tdx_clflush_page() or
add a variant that takes one.

> +
>  	ret = seamcall_ret(TDH_MEM_PAGE_AUG, &args);
>  
>  	*ext_err1 = args.rcx;