I am new to Shadows in D3D9/10/11

I have been following this tutorial which is quite clear:

https://takinginitiative.wordpress.com/2011/05/15/directx10-tutorial-10-shadow-mapping/

Let's say you have drawn the scene with couple hundred of draw calls and you are about to render the shadows. The vertex shader is defined as:

struct PS_INPUT
{
    float4 pos : SV_POSITION;
    float4 lpos : TEXCOORD0;        //vertex with regard to light view
    float3 normal : NORMAL;
};
 
//--------------------------------------------------------------------------------------
// Vertex Shader
//--------------------------------------------------------------------------------------
PS_INPUT VS( VS_INPUT input )
{
    PS_INPUT output;
    output.pos = mul( input.pos, mul( world, viewProj ) );
    output.normal = input.normal;
 
    //store worldspace projected to light clip space with
    //a texcoord semantic to be interpolated across the surface
    output.lpos = mul( input.pos, mul( world, lightViewProj ) );
 
    return output;
}

My question is, do you need to pass all Draw Calls again as a second pass, or there is a way to get the vertices previously drawn from the GPU or somehwere else? The former seems quite expensive in terms of performance.

Any clarification is highly appreciated.

Thanks !